Help needed: LrC will no longer import Photos or add a folder or optimize catalog

Hi! I would be grateful, if someone knows this problem and could offer a solution:
I recetnly opened LrC which I have not been using for approx. 3 months. I wanted to add a folder and import new photos.  The app would do: nothing. It does'nt crash but it just stays idle. No9 progress bar of any operations is shown.
I tried to optimize the catalog: this would take forever (over night (!)) and would not finish.  Canceling the optimization would also result that it would not stop this. It seems to hang up. I have to force LrC to stop vie Task manager.
Then I tried to delete all previews: same thing, nothing happens.
The catalog size is approx. 800 MB large. 3 Months ago, I could edit and manage my photos flawlessly with LRC. But after a few months of not using, it just would not work anymore.
LrC catalog and all fotos are on fast external SSDs with plenty of free space.

Things I have done to improve performance:
I have updated LrC and all other Adobe products to their lates version
I checked and optimized GPU settings.
I stopped all face-, address-, AI assisted recognition features
I mooved a few photos onto my local dectop - to find out if the SSD may have a problem. Same thing. It's not on the SSD...

My Desktop PC is not a high performsance machine. 8 GB RAM, 970 NVIDA graphics card. I don't expect it to "race" through the processes but coming to a complete halt is another story....
What could be done to get LrC working again? Has anyone experienced similar issues?

I'll appreciated any advice. Thanks!, Norbert from Germany.