My 2016 Imac Big Sur install - Now A dog!

Notes:

• Adware - Adware detected. You have adware (malware). Use Malwarebytes for Mac (free) to remove.
• Security updates disabled - Security updates are disabled. This computer is at risk of malware infection and Apple security disabled - Apple security software is disabled. This computer is at risk of malware infection. PLEASE re-enable these!
• Clean up - There are orphan files that could be removed. Follow the EtreCheck prompts to remove orphan files.
• Delete TotalAV. Instructions
• You have lots of Internet Plug-Ins. These can cause issues.
• Paragon Software should not be used.

Now, startup in Safe Mode, Start up your Mac in safe mode - Apple Support, login, and restart into normal mode. Test the speed, and generate a new EtreCheck report.

Cheers,

Jack

There is no late 2016 iMac. There are 2015 models and 2017 models.

I believe we need to proceed with an EtreCheck report. EtreCheck is a useful App to and identify issues, both hardware and software. It is trusted by many users. Please follow the steps outlined below:

1. Navigate to: https://etrecheck.com and get the free version of EtreCheckPro.
2. Download it. It is a free and trusted app. It is often recommended here on Apple Support Communities. 
3. Open EtreCheck, and before running the report, be sure to check “Allow full Drive Access” at the bottom of the EtreCheckPro window.
4. Run the report, and put it in a post, as seen here: https://discussions.apple.com/docs/DOC-250000211. We will then examine the report for issues in your Mac.

Cheers,

Jack

Notes from your EtreCheck report:

• TotalAV is still installed. Please delete according to the developer's instructions. [Instructions]
• AppCleaner still appears to be installed. Please delete.

Now, startup in Safe Mode, Start up your Mac in safe mode - Apple Support, login, and restart into normal mode. Test the speed.

However, something appears to be amiss with your Fusion Drive;

Performance:

System Load: 2.14 (1 min ago) 1.71 (5 min ago) 1.53 (15 min ago)

Nominal I/O speed: 59.91 MB/s

File system: 19.10 seconds

Write speed: 308 MB/s

Read speed: 650 MB/s

As Allan J. said earlier, these scores should be higher.

Please use DriveDx to get a report on the health of your drives. Then, upload the report here.

Also, please Use Apple Diagnostics to test your Mac - Apple Support, and let us know the Reference Code when done.

-Jack

Sorry to be late the to party. Jack is doing a fine job.

In reviewing your drive config and its performance numbers, I see a serious issue with your Fusion drive:

Performance:

System Load: 1.29 (1 min ago) 2.05 (5 min ago) 2.17 (15 min ago)

Nominal I/O speed: 0.13 MB/s

File system: 19.87 seconds

Write speed: 280 MB/s

Read speed: 708 MB/s

Those two numbers are far below what I expect to see a Fusion show for either metric. This is from an EtreCheck report produced by a 2015 iMac 27 5K with a Fusions drive, which was itself slower than many fusion drives:

Performance:

System Load: 0.92 (1 min ago) 1.71 (5 min ago) 1.27 (15 min ago)

Nominal I/O speed: 10.20 MB/s

File system: 20.97 seconds

Write speed: 520 MB/s

Read speed: 2005 MB/s

The drive's hardware specs are roughly the same as yours.

Although I do not think this is your issue, it is good practice at this point to eliminate the possibility of a "split" Fusion drive, where the SSD part and the rotational part stop communicating via software:

How to fix a split Fusion Drive - Apple Support

Once you remove the useless items Jack identifies, including "AppCleaner," please run a new test and post. I have see many posts here where unneeded AV and so-called 'cleaning" apps slowed drive performance. It is hard to tell from the first report if the fearware is masking the drive's true capabilities or problems.

EDIT: An incidental finding:

3rd Party Preference Panes:

Flip4Mac WMV (? - installed 2013-03-30)

Paragon NTFS for Mac (Paragon Software GmbH - installed 2016-12-01)

Perian (? - installed 2011-07-24)

Both are older than your computer and likely moved by Migration Assistant (that is why I don't use MI) from an older computer. If you need these, update them to current; if not, dump them There is some evidence that outdated video software, plugs, and extensions can slow down Macs.

Your hard drive is failing. Please backup all data ASAP!

You essentially have two options from here:

Option 1: Get the hard drive repaired. You can make an appointment at an Apple Store and get the hard drive repaired. If you go this route, make the Genius Bar appointment here: Get Support. However, Apple considers your Mac vintage, and Apple may or may not have the parts to fix it.

Option 2: Run macOS (and your data) from an external SSD: If you go this route, you run the operating system (macOS) and have your data on an external SSD connected to your iMac. For more info, instructions, and what external SSD to buy, please read: How to Setup and Use an External SSD as y… - Apple Community.

-Jack

Where do you notice the slow downs? Opening Apps, opening document, etc.?

What apps give you slow performance?

Cheers,

Jack

Can you also please upload the DriveDx report for the HDD portion of the Fusion Drive?

-Jack