macOS Catalina 10.15.3: Privacy Tab Does not Work — Files and Folders Inoperable

I can’t fathom what it means that the "+" and "-" button are disabled in Preferences => Security & Privacy => Privacy—yet another macOS Crapalina bug.

Is the Files and Folders area dependent on something else to operate, and if so, which settings, and why doesn’t it say so?

Thus at present the only way I can allow an app to have access to anything is to give it Full Disk Access, which does function... well sort of, sometimes and partially.

Inoperable Files and Folders in macOS Catalina 10.15.3