Slow iMac

I believe we need to proceed with an EtreCheck report. EtreCheck is a useful App to diagnose 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.

Jack

System Preferences - Users & Groups - Select the user - click Login Items

EtreCheck purges any personal or security information from itself before creating a report. The app was expressly designed to SAFELY display important diagnostic info in these forums while protecting your identity. It is the only effective way we who help here can make recommendations for computers we can neither see nor touch.

Any other way you have in mind?

The only other option is this text-based venue is for us to play a protracted game of "20 Questions" with you that will definitely keep some knowledgeable people from contributing and extend the time it takes to resolve the issue. Beyond that, the remaining option is to take the computer to an Apple Authorized Service Provider or independent service person.

Also, we know the developer. He is one of the most respected contributors here.

Your call.

EtreCheck reports do not contain any personal information what so ever and has been that way since it's original release many years ago now. If you are unwilling to post your report that is okay, however there is little we can do to help you as we cannot tell what has been installed or see any clues about your system.

Please let us know how you would like to proceed.