

VNC? You have your choice of servers, and clients are ubiquitous.
A big gotcha is that you need to be careful with encryption/security, as in classic UNIX style VNC does one thing (remote desktops). It’s easy to forward over ssh though.
You can also use VNC to share, which is not what you want; this depends on the type of server/settings. But you can definitely create a new virtual X11 session and access it remotely.

Not the same, but for my Immich backup I have a raspberry pi and an HDD with family (remote).
Backup is rsync, and a simple script to make ZFS snapshots (retaining X daily, Y weekly). Connected via “raw” WireGuard.
Setup works well, although it’s never been needed.