files not opening. OS 12.1.

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac 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

Also have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Poltergeister wrote:

files not opening. OS 12.1.

The current stable release of Monterey is macOS 12.2

Keep your Mac up to date - Apple Support

https://support.apple.com/guide/mac-help/get-macos-updates-mchlpx1065/mac

Do you have a Rescue Plan In-Place. This comprises having 3 Backups using 2 methods and 1 Off Site incase of Theft, Loss or Natural Disasters.

A Time Machine Backup  is very useful and can be used to Revert to Previous Working macOS.

For additional purposes - two Tested Bootable Clones each to separate external drives. This is insurance incase the upgrades goes sideways. At least one Tested Clone and / or Time Machine Backup should be Off - Site