perhaps you could explain exactly what happened here. Was this just a monthly update? What happened in Thunderbird when you opened it?

Yes, it was the monthly update (Windows ver 1909, OS build 18363.1556). It took a little longer than normal to complete, but not unusual. After restart, I opened Thunderbird. The program opened normally, but all my accounts and associated data were deleted. Reset my accounts and everything worked normally. I then tried to load the old emails from the file folder in appdata. My first time dealing with this and I thought I followed the directions correctly, but nothing came back into Thunderbird.

Thanks for getting back to me; please let me know if you need more info.