That folder name should logically only be randomly generated when the backup folder is first created. I don’t think that folder name would change, at least all of the other backup plugins don’t do that. They generate a unique/random folder name and that folder name stays the same.
Regular Expressions code (wildcards) canNOT be used in ARQ exclude rules. The folder name/path needs to be exact due to the way these checks need to be done/required by PHP rules in general for the code that is used to do these checks.
The exclude rule would be: backupwordpress-12755e2451-backups
Another and probably better option would be to change the path in BackUpWordPress options/settings and have the backups be stored under the /bps-backup folder. The /bps-backup folder is excluded by default and the /bps-backup folder is already protected with Deny All .htaccess file protection. Only you can access the /bps-backup folder and no one else. You would NOT need to create an ARQ Exclude rule since the /bps-backup folder is already excluded from being checked by ARQ by default.
Create a folder named: /website-backups/ under the /bps-backup folder
Change the BackUpWordPress options/settings backup folder path to this folder path.
Example: /bps-backup/website-backups/ your backups would be stored here