a folder is created in the base directory of your remote space for the backup at
/.AndroidBackup
if you delete that permanently (empty the trash), at best the free disk space should recover.
In the past, both the web info stats on available space and the device side widget took time to update that status. You might need to reboot the latter.
The upstream package to foundation.e.backup (Seedvault) was able to do device local backups and also exclude on an app-by-app basis. I think this could come back to the downtream version.