Desktop files and folders not responding to double-click (2019 iMac Catalina)

Perhaps it is the mouse or trackpad?

Boot into Safe Mode and see if it still happens. Safe Mode is klunky and takes a long time to boot up. It will prevent certain things from running which might be interfering with the mouse inputs.

If the Safe boot doesn't help the problem download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Add Text button to include the report in your reply. How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck Privacy preference pane so that it can get additional information from the Console and log files for the report:

ALSO IMPORTANT:

Then we can examine the report and see if we can determine the root of the problem.

I don't see any of the usual suspects in the report. There are 3 possible fixes you can try:

1 - download and apply the macOS Catalina 10.15.4 Combo Update. 

2 - if #1 fails boot into the Recovery volume (boot with the Command + R keys held down), select Disk Utility and run first aid on the boot drive.

3 - lastly if still not fixed boot again into the Recovery volume (boot with the Command + R keys held down) and reinstall the system. Do not erase the drive but just reinstall the system. This will not remove your user data files but it's wise to have a current and full backup before attempting in any case.

I am having the same problem as the person initiating this message. I used an iMac for many years until it was so bad I replaced it with a new one. I upgraded OS to Catalina and noticed double click didn't do anything. I've explored all I know but it continues. I've ordered the trackpad to use instead but would appreciate seeing how this is resolved so I can too fix my machine.

I tried safe mode but the problem is still there. The update 10.15.4 won't run for me. I used Disk Utility to run first aid and no problems were found. Restarted in Recovery and reinstalled Catalina. Double click still doesn't work. I see the problem trying to add a new event to my calendar and when I try to edit an event on my calendar. Also, I play games on Pogo and the solitaire has stopped allowing me to move more than one card to another stack. If there are other suggestions that I should try, please let me know. I did get the extended warranty on the new machine so I can contact Apple Care. You all are so helpful and responsive, I appreciate your advice.

2 - if #1 fails boot into the Recovery volume (boot with the Command + R keys held down), select Disk Utility and run first aid on the boot drive.

3 - lastly if still not fixed boot again into the Recovery volume (boot with the Command + R keys held down) and reinstall the system. Do not erase the drive but just reinstall the system. This will not remove your user data files but it's wise to have a current and full backup before attempting in any case.

These two.

If it's working OK after the Safe boot then don't try the others unless the problem comes back.

I don't see any of the usual suspects in the report.

Have you tried the two Recovery volume items?

Have I tried to do what to the two Recovery volume items?

Old Toad, thank you for all your help. I've done all you suggested and find I need to contact the Apple Care folks. I just got my new Magic Trackpad but that didn't help.

Thank you again.