iMac running slow

Please determine if the same problems occur in "Safe Mode": How to use safe mode on your Mac - Apple Support.

Drives:

disk0 - APPLE HDD HTS541010A9E632 1.00 TB (Mechanical - 5400 RPM)

That mechanical hard disk drive may be a performance limiting factor, and it may be operating in a state of failure. It should not have taken so long for EtreCheck to run, but the file system performance seems relatively ok. In other words it's not conclusive.

Conclusively diagnosing hard disk drive failure is not a straightforward task, and a Mac can run for a very long time with a hard disk drive in a failed operational state. However, if the Mac runs just as poorly in Safe Mode as it does normally, the possibility of disk failure becomes an increasingly likely cause.

A more conclusive test can be conducted by installing macOS on an external hard disk drive, but the first order of business is to create a backup since that report indicates Time Machine is not being used. To learn how to use Time Machine please read Back up your files with Time Machine on Mac - Apple Support.

macOS Big Sur 11.7 (20G817)

Update macOS. To learn how to do that please read Update macOS on Mac - Apple Support. It is possible that alone will fix the problem.

Welcome!

The reason your iMac is slow is due to the 5400-rpm hard drive:

Drives:

disk0 - APPLE HDD HTS541010A9E632 1.00 TB (Mechanical - 5400 RPM) - ⚠️

While this hard drive found in your Mac is perfectly suited to light tasks, such as email, web browsing, etc., for more advanced tasks, and for users who want the maximum performance from their Mac, this hard drive does have its limitations. Luckily, you can use an external SSD as your startup disk to run macOS and all your data from that. It will make your Mac 10 to 40 times faster for storage, and in turn, make your entire Mac system much faster. For more info, instructions, and what external SSD to buy, please see: How to Setup and Use an External SSD as your Startup Disk on a Desktop Mac - Apple Community.

Another option is to replace this Mac with a new Apple Silicon Mac: Mac - Apple. You can also use Apple Trade-In to get credit towards a new Mac: Apple Trade In - Apple.

Jack