Not being an Nvidia user, I can neither confirm or deny, but if it doesn’t work that way, perhaps it should.
Often, one of the problems with downgrading, blacklisting, and repeatedly restoring snapshots only to repeat the same process over and over again, is that we can be left in what’s generally referred to as an unsupported partial upgrade state where more problems might be caused than those one is attempting to fix.
This comment is why I suspect there might be other contributing factors;
You have sddm in the mix.
The following was listed in a recent Known Issues and Solutions section of an Update announcement:
There was also the following in the Unstable or Testing branch.
It’s not mentioned whether you might have switched to another branch temporarily in an attempt to solve your issue; just as it’s uncertain whether this is still relevant in Stable, but the symptoms seem to potentially fit:
