Backup is not a tool. Backup is not a software you can buy. Backup is a strategy you need to study and implement to be able to solve your specific problems.
If you are using Proxmox, ZFS is one of the best local storage options. You can easily backup your lxc containers using Borg.
Raspberry PI i4 s a great platform for FreeBSD but if u-boot detects there's a powered hub, the boot seems to go crazy. It isn’t even able to recognize the SD partitions. The result is that the Rpi4 won’t boot and start loop.
Lxc containers are fast, small and useful. Proxmox Backup Server is quite slow with them, so here's how to perform a fast and efficient backup using Borg.
Proxmox Backup Server (PBS) has been released. It's still in beta but is already perfectly usable. After many years, it's now possible to perform incremental backups of the VMs and thanks to the qemu dirty bitmaps, backups are also fast.