Michael, I don't know how to fix the current problem but I can help you from getting into these situations in the future.
Backup Backup Backup
Before you start making changes to your OS, you need to make a bare metal backup.
The easiest way to accomplish this is to clone the OS drive.
After you clone, then if you screw up the Os you can just do a reverse clone and you are back to where you started.
Also you need to stop doing open heart surgery, for an ingrown toenail. If you're having issues with darktable, post a question about the problem, upgrading the OS seems like overkill.
I've mentioned this before, you should look at running your system in a virtual machine.
Then before making changes to the system you can take a snapshot, make the changes and then test them. If things go wrong, you just reboot to the previous snapshot, if all is fine after a week, you can delete the old snapshot.
You could also clone the virtual system and do testing in the clone before updating the original.
Backup Backup Backup
If you had a bare metal backup, you'd be up and running already.
Hope this helps for the future.