I am speaking here of a particular solution, not a general one. In Proxmox VE, backups of VMs can be performed in three modes: stop mode, suspend mode and snapshot mode. They differ by the length of VM downtime and the risk of losing consistency: https://pve.proxmox.com/wiki/Backup_and_Restore

Then, there is Borg, a highly performant non-snapshotting deduplicating backup tool: https://borgbackup.readthedocs.io/en/stable/deployment/image-backup.html There is also a wrapper for Borg, called Borgmatic, for ease of configuration and execution: https://torsion.org/borgmatic/