Upgraded to Classic 10. Old catalog updated. Now all photos are missing.

Hi,

Today I upgraded Lightroom Classic to version 10. Everything was working perfectly fine at first. But when I tried to open my 2019 catalog, I was prompted to upgrade it. I went ahead with the upgrade and now none of my files can be found. Just a bunch of blank thumbnails. In addition, the filename that displays for each photo is the default name the camera generates. Further, it appears that I'm missing some collections. I've included a screen shot.

When I check my hard drive, everything looks fine; I can see all the photos and the filenames are what I changed them to long ago. The only change I made to my hard drive was upgrading my OS to Big Sur yesterday.

My 2020 catalog appears to be working OK. I have not checked any of my remaining catalogs because I don't want to wind up with a bunch more "lost" files.

What in the world happened?

Thank you very much!