If you are trying to put your "back up catalog" on the same drive as the regular catalog, you are risking having the drive crash and have zero catalog.
My LR application and my catalog (lrcat file) are on my internal drive, and when I close LR, i have it back up the catalog to an external drive - ( I also then clone that drive to another to have two back up copies.)
Still your problem does not seem correct. Can you try to manually copy the LR catalog file and ALL the files in the LR folder (not the photo files themselves) and copy them to a second location for safety.
Then can you try :
Resetting the preferences for LR by:
then just hold down Alt and Shift (Windows) / Opt and Shift (Mac) while opening Lightroom and it’ll ask whether to reset the preferences. The timing is crucial—hold them down while clicking/double-clicking on the app/shortcut.
It will ask if you want to reset the prefs, ay. yes and continue.