App Store goes unresponsive after switching user back and forth macOS Catalina.

Try resetting SMC and NVRAM and then boot into Safe Mode by starting up holding Command S. It's a long boot because macOS does some maintenance under the hood and can solve some problems. It does things like deleting cache files, reorganizing boot structures, etc.

Also try logging off of your iCloud account on the Mac and logging back in.

There are no recommendations on how often to reset SMC and NVRAM. They are procedures more used to try solving problems.

You should likely consider performing a clean install of the macOS, getting rid of any old files and settings that might be driving your Mac a bit crazy.