I logged into my world, and it automatically updated to 1.16.5 Release candidate 1.  It usually asks if I want to back up the world when it switches versions but it didn't.  Then, once logged in, I was missing the following:
All Villagers regardless of whether they were traded with or not.  Approximately 60 were just gone.

All named mobs were gone

All item frames that were placed were gone

All path blocks were gone

All items in item frames were gone.