EFI 1.8 “This software is not supported by your system” on iMac 21.5 2010

Apple updates the system firmware both SMC & BootROM through macOS updates. If you have installed macOS 10.13.6, then the iMac should be on the latest firmware. You can use the links provided by @BDAqua & @MrHoffman to confirm if your iMac is running the latest firmware.

Those old firmware updater links are very old and won't give you the latest firmware for the system. Plus when the requirements mention macOS 10.6.7, then it literally means only 10.6.7, not 10.6.7 or later....those firmware updates are OS specific. So if a firmware update was provided for only macOS 10.6.7, then that firmware revision would be extremely old. In fact macOS 10.12.4 updated the firmware to allow for access to Internet Recovery Mode, the online Apple Diagnostics, and knowledge of the APFS file system for booting.

I don't know what tool you are using in those screenshots, but if it is the Apple firmware updater, then it probably does not recognize the major changes made to the firmware by later versions of macOS. Post a screenshot of the Apple System Profiler showing the hardware information and the firmware revisions both for the SMC & BootROM....just make sure to edit out the system serial number from the screenshot.

If your system is slow, then the expanded 16GB of RAM would be one possibility since Macs are very picky about the memory they use.

Which Crucial SSD are you using in this iMac? If it is the BX500 series, then that can easily be the problem since the BX500 SSD is pure junk since it can perform worse than a hard drive. The Crucial MX500 series is good and should work fine. Or use the OWC Mercury Electra 3G SSD which utilizes only a SATA II controller so there should be no issues auto negotiating the SATA Link speed which can happen with some SATA III SSDs. This is why OWC is still providing SATA II based SSDs (hence the 3G designation for 3Gb/s the SATA II max speed).

Have you tried running the Apple Diagnostics to see if any hardware issues are detected?

If you have an SSD other than the BX500 series, then you can check the health of the SSD by running DriveDx (free trial period) and posting the complete text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar so I can review it.

Justacrappyrepairer wrote:

I am using a MX500 drive that I ripped out of a windows computer and formatted it, so on every other computer I’ve gotten good read/write speeds except this computer.

Run DriveDx (free trial period) to check the health of the SSD and post the complete text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar.

I would not expect the MX500 to have any compatibility problems with a 2010 iMac, but I also never used one there either although I have installed them into 2010 laptops without any issues. Not all SSDs are compatible with all hardware/computers.

I’ll try maxing out the ram although it may not make that much difference.

More memory won't help. If anything the existing memory may have a bad module. No need to purchase more memory at this time since it is easier to run a memory test and remove individual sticks to see if one of them is causing a problem. Creating & using a bootable MemTest86 USB will help check the memory.

I attempted to use the Apple hardware diagnostics to find the problem by a bootable usb program as the original one no longer existed due to not having the original disk. Although when it was going through the “Probing your hardware, this may take a minute”, everything froze, not even the mouse was moving.

Your system firmware is using the newer style firmware associated with macOS 10.12.4+ so this iMac should have access to the online Apple Diagnostics. I don't know what USB program you are using, so cannot comment on that, but if it is an official Apple Diagnostic, then that freezing would indicate a hardware issue of some sort. Whether 99.0.0.0.0 is the latest BootROM firmware for this particular iMac, I don't know. You would need to use the eclecticlight.co link that @BDAqua provided to confirm as that is the only source which tries to document the latest firmware for various Macs since Apple stopped doing so some years ago.

Even when I booted into it, it was lagging heavily, having to wait around 3 seconds for the screen to refresh and show my mouse in its new spot if I moved it.This happens when I try to run things off a bootable usb etc open core legacy, EFI boots for other items such as the MacBRTool, and more

Completely remove Open Core Legacy Patcher from the system and test again with a macOS 10.13 High Sierra install. We have no idea how using OCLP will affect this iMac or any bootable USB media, nor how a later unsupported version of macOS will behave. There is a reason why Apple does not officially support later operating systems, usually because the older hardware is missing a critical component such as a CPU hardware instruction, or GPU feature, etc. It may even be affecting the ability to access the online Apple Diagnostics. I do know from a very brief reading of the OCLP documentation that it modifies the PRAM in order to make things work so you would need to clear the PRAM as well. No one can help you if you are using OCLP since the moderators will remove any discussions that try to make it work since it is against the forums Terms & Conditions. You will need to look elsewhere for that type of support.

I see several additional items in addition to what @BDAqua mentions.

The firmware of the MX500 SSD is out of date. You should update the SSD's firmware to version M3CR023 (select M3CR010 from the dropdown list which will give you a link to the proper firmware):

https://www.crucial.com/support/ssd-support/mx500-support

Extract the ISO file from the downloaded ZIP file and use the ISO file as a source for Etcher (Mac, Windows, Linux) which will make the bootable Crucial firmware USB updater. You will need to Option Boot the Crucial firmware USB stick by holding down the Option key immediately after hearing the Startup Chime. Select the orange icon labeled "EFI".

FYI, make sure to have a good backup of any important data on the SSD since a firmware update is always a risky proposition although this firmware update should not normally affect the data on the SSD. The Crucial website has a warning about this on the MX500 support page I linked.

I also see the SSD's Lifetime Max temperature reached 69C which is just short of the 70C threshold where the SSD will be throttled. The temp is still below 100C "Recommended Max Temp" and "Temperature Max Limit" values assuming DriveDx is accurately reporting them here. I don't recall seeing 100C for these values on my SSDs, but my SSDs also have later firmware.

Otherwise the SSD looks healthy, but TRIM probably should be enabled by using the command line and the following command:

sudo  trimforce  enable

This will prompt you for your admin password. Nothing will appear on the screen as you type the password, so just press the Return key to submit the password.

The other thing I notice is the memory is not installed correctly. The system logs seem to also show memory related issues (4 different log entries). The two matched pairs of memory should be in either the same Bank# or in the same DIMM# slots. I'm not sure what is correct for this laptop. I would first try placing the 4GB modules into DIMM 0 slots and the 2GB modules in the DIMM 1 slots to see how things go. I know on some iMacs that they may need to go into the Bank 0 and Bank 1 slots instead. IIRC, the default from the factory is DIMM 0 slots being filled first, at least I believe that is what I've seen most often in the posted EtreCheck reports where just two modules are involved.

It also appears there may be a Spotlight Indexing issue, so you may want to rebuild the Spotlight Index:

Rebuild the Spotlight index on your Mac - Apple Support

I would even suggest trying to run Disk Utility First Aid on the hidden Container first before rebuilding the Spotlight Index. Within Disk Utility you may need to click "View" and select "Show All Devices" before the hidden Container appears on the left pane of Disk Utility. I would also recommend moving the memory modules to the positions I suggested to lessen the chance of a memory issue interfering with the First Aid scan & Spotlight Index rebuild.

Mal-S has a good point, there are apps that will prevent an update in the past, Firmware Updates almost always come in Security Updates.

Check System Report>Software>Installions>Security.

In mine you'll see repeated ones because even though it said Installed it didn'y actuall finish, & it was because of other SW interfering...

See which wasthe last installed & try applyng the latest Sedurity Update again, but whilst booted in Safe Made.

https://theapplewiki.com/wiki/Mac_Security_Updates

Check what is loading at boot time , these could be apps, deamons, helper programs etc. Previously deleted apps often leave behind things which still load in the background. Uninstall any antri-virus or cleanup apps, they aren't needed and can cause issues.

Have you run Disk Utility's Disk First Aid on all connected drives?

In Disk Utility>View, select Show all Devices, highlight the top left entry.

Run Disk First Aid on all items in the left panel, from top down.

Are you running any VPN, Anti-Virus, or Cleaning apps?

We need to see what all is running, a report from this will not display any personal info...

Using EtreCheck - Apple Community

EtreCheck is a FREE simple little diagnostic tool to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac. It will not display any personal info. Give it Full Disk Access.

https://www.etrecheck.com/

Thanks for Old Toad’s etrecheck instructions…

Slow iMac 2017 - Apple Community

In the future you might run the free app SilentKnight from The Electric Light Company. It scans your system and indicates which of the various components of the system are up to date and which need installing to the latest version. It will do that for you, including EFI:

I run it after every system update and upgrade. The ELLC is a highly respected group with many free utilities for MacOS.

Maybe this helps?

About EFI and SMC firmware updates for Intel-based Mac computers - Apple Support

Or this?

iMac EFI Update 1.6 - Apple Support

There’s a MacBRTool around too, but whether that works? Or whether it bricks this iMac11,1?

An SSD — even on SATA 3.0 Gbps — will still be preferable to an HDD, in terms of performance.

And yes, other issues with the Mac, its cabling, or the SSD can all cause performance issues.

Apple Diagnostics might find some issues, or (better in various ways for this task) so might DriveDx.

Regarding the boot speed: have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on the Mac?

• What version EFI is it on now, I find that iMac11,2 has 005D 00B as the latest.

https://eclecticlight.co/2018/06/27/which-efi-firmware-should-your-mac-be-using-version-2/

Reinstall without all the hacks (OCLP, fan controls, boot flags, etc), and enable trim on the SSD, and test again.

According to MacTracker, an iMac (21.5-inch, Mid 2010) has

• A 3.0 Gbps SATA interface (3.0 Gbps = 375 MBps before overhead)
• USB 2 ports
• A Firewire 800 port

Most newer machines with SATA interfaces would have 6.0 Gbps SATA ones. The difference between SATA-II and SATA-III might not matter much for a mechanical hard drive, but if you are basing your expectations of SSD speed on systems with SATA-III interfaces, you might be disappointed.

Justacrappyrepairer wrote:

Okay, so hypothetically it would be better just switching back to a hard drive.

No! I concur with MrHoffman, that the SSD will be faster than an HDD.

The question I have, is what SSD did you guy's use to upgrade the 2010 iMac's.