I have looked into my router and restarted it several times, and I see nothing weird here. The rest of the devices on the network (and even this same computer if I boot from Windows) can connect via ssh without difficulties. I’m going to try and create a DMZ for this machine, though. Just to be completely sure the router isn’t playing any games.
I confirmed from the server (connecting from my laptop) that no ssh connection request is arriving from my ip, as I suspected. For some reason, ssh command doesn’t make the call.
If only I had read you before installing Ubuntu… I promise I tried everything on my hand to get this to work, but in the end I gave myself up and switched back to Ubuntu.
I will try your solution on a Live USB, though, because I prefer Manjaro. If it works, I will definitely go back.