Sticky mouse makes mac inoperable

Try the following in order as needed:

1 - Reset NVRAM or PRAM on your Mac - Apple Support 2-3 times in succession.

2 - boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and test to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Did you try a different mouse? It clearly seems to be a mechanical problem...

Hello 42n8guy,

Thanks for using Apple Support Communities! We see you have an issue with the mouse you're using with your iMac, and we'd like to help.

Have you tried to safely clean your mouse yet? Here's how: How to clean your Apple products

Select "Peripherals" to get to that section.

If you're still having the same issue after cleaning, try using a different peripheral device to see if the issue continues. If not, it may be time to replace your mouse. Apple Online Sales - Mac Accessories - Mice

Take care!

Is the Mouse a Third Party mouse ? Is there Third Party software installed to control the mouse ?

If yes to both, has one verifies with the Manufacture of this mouse for updated and compatible Software for the version of macOS installed on the computer ?