The best metaphor is "tmux for X programs": the X server runs on the same host as the X programs, xpra then "forwards" the windows over a configurable transport

The best metaphor is "tmux for X programs": the X server runs on the same host as the X programs, xpra then "forwards" the windows over a configurable transport (e.g. via SSH) to the client. X was IIRC intended for local networks, so forwarding it over the Internet is sloooow (both by verbose protocol and naive latency handling) - this takes care of both issues. IIRC it's written in Python, so it runs in most places: https://xpra.org/ https://xpra.org/