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Sort of hard to give any specific recommendation - make sure if the port is open, see if NTT is not being blocked by a firewall or anything (does WINE get it's own firewall? Been a while since I used it). I guess there's Hamachi and similar in worst case scenario - I think they still offer some sort of a simple client for Linux?

It doesn't seem as though it is. And I've had very negative experiences with Hamachi in the past so I'm very reluctant to try it when I've successfully portforwarded anyways.

In that case I'd suggest to ask on Discord (discord.gg/nt) as I have slightly limited number of guesses on this subject