It's not a video coding issue. I looked at what format was acceptable back in 2019 and have uploaded several videos all in mp4 format with no problems until today.

I did some detective work. Dick Tracy is on the case. That was my nickname when I was in school many moon ago. It seems to be a Windows 10 or Firefox problem on the computer I am currently using. I powered up an older computer with Win 7 and with Firefox. The video player shows up and videos play fine.  It has nothing to do with the changes so I apologize for assuming it was due to the site changes. (Hangs head in shame).  Not knowing what to look for is going to make it difficult to solve the problem. I'll figure it out eventually.