For me, it's case-by-case. I don't back up the VMs directly, just the data of the stateful applications running on the VMs (or bare metal servers, I do identical stuff for them).
For postgres, I used to just have a systemd timer that would `pg_dumpall` and throw it in s3.
For other local files, I use borg backup for personal files and services I just run for myself, and I use restic to backup server files to s3.
The operating system's configuration is all stored in git via the magic of NixOS, so I don't have to worry about files in /etc, they all are 100% reproducible from my NixOS configuration.
For postgres, I used to just have a systemd timer that would `pg_dumpall` and throw it in s3.
Now I use https://github.com/wal-g/wal-g to backup my postgresql databases.
For other local files, I use borg backup for personal files and services I just run for myself, and I use restic to backup server files to s3.
The operating system's configuration is all stored in git via the magic of NixOS, so I don't have to worry about files in /etc, they all are 100% reproducible from my NixOS configuration.