"System Preferences - Privacy & Security - Files and Folders" on Catalina seems locked

Hello, ChipGore.

Welcome to Apple Support Communities.

From what I've read and understand is that you're unable to make changes to Files and Folders in System Preferences. I'd like to help. See if repairing your permissions helps using the steps in this article: Resolve issues caused by changing the permissions of items in your home folder

If that doesn't help, run Disk Utility for First Aid and check your hard drive: Repair a storage device in Disk Utility on Mac

You can also see if the same thing occurs in safe mode and a test user account:

How to test an issue in another user account on your Mac

Use safe mode to isolate issues with your Mac

Keep me updated.

Cheers!

Verify you have unlocked the padlock...

Typically apps are added here via launching the application, you may have to check the app to give it permission

after you add to Full Disk access

Change Privacy preferences on Mac - Apple Support

Control access to your files and folders on Mac - Apple Support

ChipGore wrote: The "+/-" are greyed out only for this option).

Once Added to Full Disk Access it will appear in Files & Folders—here you may have some additional check boxes, and Full Disk can be unchecked if you see fit:

ex compare BBedit.app

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Followed every single instruction. Still having the same issue.

Of course i have the padlock unlocked... like @ChipGore said before "....The "+/-" are greyed out..." for the Files and Folders option.