This is actually Sarah, hi.
There have been a slew of strange problems happening for a lot of folks upgrading to the new Lightroom version. I helped another grad with a similar problem yesterday where all of her 2020 images were gone from her upgraded catalog. It turned out that there were two catalogs in her Lightroom Catalog folder that were nearly identical but one of them had 2020 in it and one did not. We thought it was a random mistake from a while back, but it’s possible you have one too?
What had happened, in her case, was that she accidentally upgraded the version of her catalog that did not have 2020 images in it. Once we upgraded the second catalog in the folder that DID have 2020 images in it, we deleted the other version and it was cleaned up.
If this isn’t the case for you, it’s possible you could have gotten some sort of bug. I would go to the Creative Cloud app and revert your Lightroom version back to the previous version and then try to open your (non-v10) catalog file and see if it contains the 2020 images you’re looking for. Then maybe wait a few weeks before updating your LR version again so that hopefully all the kinks will be gone by then.