Chatted with Apple Support.
We worked through some stuff and eventually got things to work.
Tried deleting a 'tcc.db' file but system wouldn't allow (even though I'm an admin), but that didn't work.
Eventually had to boot into recovery mode and enter a command in Terminal that negated the safety precautions in the system. Went back into OS (again, 13.6.1) and all my accessibility and full disk access were there again.
We then went back into Terminal and re-enabled the security stuff, booted back in OS and everything was, again, there.
The support guy said they've been seeing a few of this issue with Settings preferences (privacy and security, etc.) not working right.
SIDE QUESTION: Would Little Snitch running have anything to do with this type of problem. I've heard elsewhere that Little Snitch can cause system issues.