QuickTime problems since Catalina update

I think several people have had this issue, but I haven't see a solution provided yet. Prior to updating to Catalina, I was able to routinely open .avi files in QuickTime Player. It would convert the file into a .mov, which was perfect for me to be able to quickly get my data videos into a more accessible format. Since updating to Catalina, QuickTime 10 gives the error "The document "blah" could not be opened. The file isn't compatible with QuickTime Player." Also, I have recently found that some old .mov files give the same error. Is there a fix or previous version of QT we can use to get around this? Or is the solution paying for full QT access or other software? Thanks!