I think there is some info missing. You’re using SSH to access the server where you are running the docker image? Why does your server have X server installed?

I have no experience running Lemmy. It could be the Lemmy instance includes X server to run some kind of GUI? Seems strange.

Correct

https://maps.app.goo.gl/tbRoqUgh7VswsVBF9?g_st=ic

We need answers!

You could check your systemd logs with sudo journalctl > logs.txt Search that file for your application name.

Otherwise try running the application from terminal, and view any logs that output.

flatpak run {app name}

You might need to add options for logging.

My guess is it’s missing some gtk assets.