darktable 3.8 flakey, where can I find the last 3.6 for windows?

Okay, it seems you have successfully downgraded to 3.6.1. Un-installing and re-installing (as @Cranky has suggested) shouldn’t be needed.

From what I’m reading, especially the:

Suggests that darktable is somehow running in the background. Have you added it to your autostart sometime?

What I would do from this state is:

  1. Restart your PC to make sure darktable isn’t running. (Restart is better than shutdown and power-on)
  2. Open the file explorer and enable all file extensions being shown by removing tge check-mark of “Hide extensions for known file types” (google this term to find dozens of descriptions on how to do this)
  3. Make a backup of your darktable config folder (e.g create a zip file with the current content)
  4. Rename (or at this point simply delete) the data.db and library.db files.
  5. Rename the data.db-pre-3.8.0 and library.db-pre-3.8.0 by clicking on one, press F2 and removing the -pre-3.8.0 part of the filename. Windows will complain that the filetype is being changed, but that’s what we want.
  6. Now open darktable and cross your fingers :crossed_fingers:

Maybe your virus scanner interferes, so you could consider disabled it while your perform above steps.