Plesk backups are overfilling the disk space. How to limit the number of server-wide backups stored in Plesk?
Via Plesk GUI
Go to Tools & Settings > Backup Manager > Settings.
Change the value of Maximum number of full backup files to store according to your needs and apply the changes.
Note: The limit is related to full and scheduled backup files only (the number of incremental or manual backups is not limited).