iMac 4K. 21.5 inch, 2019 painfully slow at everything, EtreCheck attached.

+1 on getting rid of the scamware. The Russian MacKeeper can be very hard to remove. You might see if the free version of MalwareBytes will recognize it as a "PUP" (potentially unwanted program) and allow full removal.

https://www.malwarebytes.com/mac

It is the development of a trusted contributor here; I trust it, as do many others.

With the minimum amount of RAM and a computer whose RAM is not user-upgradeable, your need to restart more often:

System Software:

macOS Monterey 12.5.1 (21G83)

Time since boot: About 25 days ⚠️

Restarting clears a lot of "deadwood." I recommend not going over 4 days.

Your hard drive is doing writes/reads at 1/2 the nominal speeds for that drive model:

Performance:

System Load: 1.53 (1 min ago) 1.33 (5 min ago) 1.15 (15 min ago)

Nominal I/O usage: 0.02 MB/s

File system: 29.83 seconds

Write speed: 38 MB/s

Read speed: 42 MB/s

Nominals are about 80MB/sec and the computer will still feel slow at that speed and newer macOS versions.

It iss possible that removing the scamware may improve drive speeds, but don't count on it. The cost-efective external solid-state drive (SSD) solution jeffrey recommends is the single best action and, if you buy the external drive with the proper specs, your w/r speeds will be around 400MB/sec. The computer wil feel quite fast at those speeds.

Proper external SSD specs:

Drive enclosure: USB3 or higher

SSD inside: SATA 6G

Thunderbolt drives are compatible with a 2019 iMac and scads faster, but are horribly expensive.

the first thing that you need to address would be removing the trusteer antivirus AND mackeeper. they are both known to cause issues within macOS while providing zero benefits. they should both be removed using the developer's instructions.

and secondly, the iMac has a 5400 RPM HDD. mechanical HDDs will run very slow on Monterey. the most cost effective way to speed things up would be to install Monterey onto an external SSD and run the Mac from it. to implement that, please see this informative user tip: How to Setup and Use an External SSD as your Startup Disk - User Tip

+1 The AV app has to go.

The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior (much like you are experiencing) and make Mac OS appear buggy. 

Please locate the developers uninstall instructions for Trusteer and follow to the letter. Then restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac and then restart normally. 

Also, the fact that you bought a base model 21.5" model which has the 5400 RPM glacially slow HD and then loaded it up with professional grade applications is a problem. If you want to keep the computer the ONLY way to make it faster is get an external SSD and make that your boot drive and take the 5400 RPM drive out of the equation. If you would like to go that route, please let us know and we can give you some instructions.

I have two of those Samsung T7 drives that I use specifically to boot my iMac into alternate macOSes when needed. they give excellent performance at a reasonable price. and they are almost twice as fast as the Samsung T5 models. and I am using the USB-C cable to connect the drives to the TB3 port on my iMac, and I am seeing these speeds.

I hope that anyone who is suffering the same as I was and comes across this discussion takes the trouble to follow the advice I was given.

Heaps of appreciation for posting such excellent follow-up information. It allows us to point other users with the same issue—and there are many—to see the impressive outcome of the simple EXT SSD option. I have it bookmarked so I can refer others to it.

Thank you!

Excellent! Thanks for the follow-up.

even if no one sees this post, running macOS from an external SSD is often recommended here because "it just works"

I'm happy to hear that you are happy. :)

Thanks!! I think this answers all my SSD transition questions!

Bill S.