Upgraded to Monterey 12.4 and my imac is way too slow

Your machine has some serious concerns.

1. Evidence shows no Time Machine (or any other type of backup) within the past 10 days. If this is correct, your data is at risk. Operating any computer without at least a daily backup is a guarantee of lost data.
2. All security has been disabled, this means you need to install Mac OS in order to repair this condition. This is CRITICAL!
3. It appears the Fusion Drive has become unfused which would seriously affect performance. Please follow Apple's instructions in How to fix a split Fusion Drive - Apple Support

These are the topics I noticed, others may see other issues that need addressing.

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community

May I know if you were able to check if any of your Apps needed an update? Also, if the iMac is Spotlight or FileVault indexing, it can slow down the Mac considerably. You can open up Spotlight search by clicking the magnifying lens at the top right of the screen and type anything in the search bar without hitting return, it will show indexing... at the top portion of the window. You can go to System Preference >  Security & Privacy > FileVault tab to check if it's indexing too.

You can also check this link for more steps:

If your Mac runs slowly - Apple Support

Hope that helps!

Etrecheck is not on the App Store because to dumb it down as they require it would not give any useable data. The developer is one of the most respected contributors to these ASC forums.

Download and run Etrecheck.  Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the first window that comes up so that it can get additional information from the Console and log files for the report:

Also click the About… vurron and read the info to further permit full disk access.

Copy the report

and use the Additional Text button to include the report in your reply.

The we can evaluate the report and see if we can determine what the culprit is.

What "Apple acceptance list" exactly are you referring to? EtreCheck was developed by a respected ASC forum member and is highly recommended by a number of us here for just this purpose. No where have I personally seen where Apple is recommending that it not be used.

However, it is really your call. If you wish not to use it, then I would suggest that you make a Genius Bar appointment at your local Apple Store or Apple Authorized Service Provider to have them take a look and provide you with your options.

EtreCheck is 100% safe and does not include any personal information in the report. It was developed by a trusted member of these forums and has been in use for years. You can download the report and examine it yourself before submitting here to vet that it is safe and has no PI.

Otherwise, no there really isn't much we can do as we cannot tell what has been done to your system to cause the problem. If you don't want to use EtreCheck, we wish you the best and hope you can find a solution to your problem.

First thing to do before re-installing Mac OS is to back up the computer using Time Machine or by creating a bootable clone backup. You need to do this to safeguard all your data just in-case of a problem.

After you back up then restart the computer while holding down Command + R which gets you into the Recovery Partition. In the Recovery Partition you will see where it says to install Mac OS, click that and follow the on-screen directions. This will fill in any missing or damaged portions of Mac OS. I suspect it also may help with your problem.

Lets see how re-installing Mac OS goes. If your problem persists then I'd like to see a fresh EtreCheck report to search for any other possible issues. If everything checks out and the report looks clean but the original problem remains the last thing to troubleshoot is the Fusion Drive itself for a hardware problem.

That likely means you have a failing External Hard Disk which should be replaced. If you are in the USA, please get an OWC Mercury Elite Pro which is a MUCH better solution than the Walmart quality Seagates, Toshibas and WD enclosures. I have that are 15 years old that work just fine.

iMac (Retina 5K, 27-inch, 2017)

iMac Model: iMac18,3

3.8 GHz Quad-Core Intel Core i5 (i5-7600K) CPU: 4-core

32 GB RAM - Upgradeable

BANK 0/DIMM0 - 16 GB DDR4 SO-DIMM 2667

BANK 0/DIMM1 - Empty

BANK 1/DIMM0 - 16 GB DDR4 SO-DIMM 2667

BANK 1/DIMM1 - Empty

Did you upgrade the RAM after purchase? A 2017 iMac 5K uses 2400mhz RAM, Sometimes faster RAM can clock back to the computer's bus speed but not always. There is another post today where installing faster RAM caused both the new RAM and the factory RAM to clock back below the machine's nomimal bus speed.

The real problem as rkaufmann87 points out is that some part of your Fusion drive is sick:

Performance:

System Load: 1.51 (1 min ago) 1.29 (5 min ago) 1.13 (15 min ago)

Nominal I/O speed: 0.04 MB/s

File system: 95.23 seconds

Write speed: 209 MB/s ⚠️

Read speed: 2423 MB/s

"Read" is right on nominals, but "Write" should be between 500 and 1000 MB/sec on a healthy Fusion Drive. The File System number is about 3x what I expect. Fusion drive data I have show File System mostly under 30 seconds with a couple or data points around 40. I do not see any software red flags so I have to think part of the Fusion system is failing, likely the mech portion.

Well the security did not install, are you sure you did a full install of Mac OS? Also, I have to agree with Allan about your Fusion Drive, this is also shown in the report. I suspect the HD is failing and needs to be replaced. My recommendation would rather than having the HD replaced to buy an external SSD, format it and then cloning your HD to the new SSD and use the SSD as your boot drive. Your other option would be to take the computer to your local independent Apple Authorized Service Provider and have the computer's Fusion Drive replaced with a dedicated SSD. If speed is your primary concern, I'd recommend the OWC Envoy Pro EX Thunderbolt 3. If you are trying to save some $$ then get a OWC Mercury On The Go Pro & OWC On the Pro Go Power Adapter

Best of luck!