Slowing iMac 2019

Please run an EtreCheck report, and share that here. Use the ‘Addition Text’ button on this forum’s reply box for inclusion of that text. That should give us most of the clues that we need to approach this.

You should follow these instructions for posting the report:

How to use the Add Text Feature When Post… - Apple Community

Also, allow full disk access, which will provide more info in the report.

In any case, there are two possible causes for your worsening performance:

(1) Fusion drive may be aging and running slower as it degrades. It relies mostly on a mechanical drive and those are extremely slow when formatted as APFS, which yours is.

https://bombich.com/blog/2019/09/12/analysis-apfs-enumeration-performance-on-rotational-hard-drives explains why this happens, the effect is striking.

(2) You have McAfee anti-virus and that can only hurt performance, especially with a mechanical drive holding most of your data and traffic. There is actually no way to get a Mac virus as the MacOS is kept in a sealed, signed read only volume. Only Apple's certified servers can modify that system now. So all McAfee does is slow down your Mac. It will be checking every byte coming across or through your system, the effect can be very significant.

I would completely uninstall (using an uninstaller from McAfee) the anti virus. This can be laborious because sometimes pieces of the software remain and have to be hunted down and removed manually.

Then check performance. If it remains poor, you could try this with an external SSD:

Use an external SSD as your startup disk … - Apple Community

To bypass the slow mechanical drive that comprises the majority of your Fusion drive.

You will need to delete the application. Then I would use Find Any File to look for "McAfee" inside contents of any file or package, across the entire Mac. You will want to delete all those. Then search for all files with "McAfee" in the file name and delete those.

You can also try typing this command in Terminal:

sudo /Library/McAfee/sma/scripts/uninstall.ch

or

sudo /Library/McAfee/cma/scripts/uninstall.ch

If these scripts don't exist, the command will not work, however.

You can also goto /Library/LaunchDaemons/ and put all files with McAfee in their name in the Trash.

Same for /Library/LaunchAgents

Same for ~/Library/LaunchAgents

Also look in ~/Library inside the /Application Support and /Preferences folders.

Others may have other suggestions ...

I also see in your Etrecheck report several other folders listed that have McAfee items listed. I would go to those folders and remove all traces of McAfee files and items.