Agonizingly slow iMac

I agree that the EtreCheck report will provide valuable information. Often times there is a specific cause and other times any of the following actions may be helpful. They are “maintenance” steps which are often ignored.

·      It is important to occasionally restart a Mac. Ideally, once a week or more often. This does some system cleaning.

·      Regularly clearing the history of your browsers can help as all the data is stored in RAM. Clearing frees up RAM for system use.

·      If your computer is set to startup with too many apps that will slow down the startup process.

·      Some programs use a lot of RAM. (Like many Adobe apps and the Chrome browser.) When using them, close any other apps not being used.

·      Doing a restart in the safe mode can clear a number of problems. This is done by holding down the Shift key at start up. This process can take up to ten minutes while the computer is doing its maintenance and cleans the cache. You may then restart normally.

·      It is also a good idea to run the Disk Utility app. If it reports some issues, then rerun it repeatedly as needed until the final report is ok.

·      On some computers the problem may simply be that there is not enough RAM installed for RAM hungry programs that are being used. The very minimum amount of RAM we would recommend for computers running the Catalina, Big Sur or Monterey OS is 16 GB. This information is found by going to the Apple logo in the upper left corner of the finder and clicking on About This Mac. Note; not all computers are able to have RAM user installed. Some upgrades must be done by a qualified Apple service specialist.

·      Last, and most important, you should remove any and all maintenance and antivirus programs. They will cause problems and will significantly slow your computer.

·      One thing that you cannot really do anything about is if your computer has an older, slow mechanical hard drive. In that case, installing an external SSD and using it as your startup drive can improve performance by up to 50%.

I hope these suggestions are helpful and enable you to speed up your computer.

At this point, I would suggest that you run an EtreCheck report, and optionally, post it here if you need assistance with interpreting its results. EtreCheck is an app that greatly helps with troubleshooting issues with Macs and was created by a valued forum member.

Ref: Using EtreCheck to Troubleshoot Potential… - Apple Community