I’m running a docker container that contains calibre ebook manager and exposes it via guacamole. It works well - a desktop app becomes available on my network, from any computer at home.

I haven't tried this yet. I did try Remotely, which is also FOSS. Remotely has an agent involved that can be installed on machines. Unfortunately it doesn't support Wayland though. Which made it a non-starter for me since literally all my machines run either headless or Wayland.