Resxt Thank you for the prompt reply!
No, I am hosting it on my (headless) server (with IP 192.168.1.2) on the same network with port 6668 (so I am using connect 192.168.1.2:6668
to connect).
Port forward is forwarding 6668 to local ip 192.168.1.2 on port 6668 (which my container also exposes).
I also tried the default port, but felt more comfortable changing it.
I did not add this in the original post since I did not want to make it any more complicated :).
Next step for me is probably running the container on the same PC where I'll be playing (not using the default port of course) to see if that eliminates the issue, which I'll be doing tomorrow.