To anyone who wants to try their luck, it is very easy with docker:
Code:
export XONOTIC_DIR_ON_HOST=/srv/xonotic
docker run --name xonotic-server -p 26000-26010:26000-26010 -p 26000-26010:26000-26010/udp --cap-add=sys_nice -v ${XONOTIC_DIR_ON_HOST}:/root/.xonotic ballerburg9005/xonotic-server-arm64
Now you can put map pk3 files in /srv/xonotic/data/ or edit the server.cfg file. Go to your internet router, find your box and open ports 26000-26010 TCP and UDP. You will then see your server in the official server list with the "hostname" you provided in the server.cfg file.
But beware: My Cortex-A55 box can only handle 4 players until it maxes out the CPU. It will also suffer from brief CPU spikes every few minutes, so that the game stutters for all players for a split second. It will consume 10-20% CPU idle. But it will not get very hot. On the map Xoylent there is a custom weapon as easter egg (Tuba). This will crash the server for unknown reasons.
I would say the Pi4 could be viable for duel servers, if it can handle the occasional CPU spikes. It would be nice if someone could actually try it.