I had the same issue recently, using VEB 18.104.22.168 on Windows 10.
I couldn't cancel, rebooting didn't help.
Uninstalling VEB and 3 SQL components didn't help either.
Resetting the database worked perfectly, using your instructions, Dima P.
I also created a write-up that might help folks, that includes a step-by-step video:https://TinkerTry.com/veeam-endpoint-backup-database-reset#steps