STUN is now always enabled.   You can try enabling UPnP on your router or manually configuring a port forwarding. There are a bunch of guides on the internet about how to do so, how exactly depends on the model of your router. There's also a section in the FAQ about it: https://gitea.wildfiregames.com/0ad/0ad/wiki/FAQ#how-to-do-port-forwarding

Last time that happened to me it was a very little detail in my router config after my internet provider made some work in the area

For the next version you should package it with the game's archive builder.  Since you're on github you can automate by adapting this action https://github.com/0ADMods/ponies-ascendant/blob/master/.github/workflows/ponies-ascendant.yml

Uh oh... I closed my account and plan to delete the mod since its outdated and I'm quite tired. I guess archive then but ye I need to dissasoiate first so I can delete my mod.io account which I don't know how.... edit: its reactivated, I'm not sure what would happen if the mod archives and me deleting my account though... Actually I can see how to archive it on my own, but... I'll wait your input.