It would be awesome cause there are no 1.17.1 mods with such option for casual non-techy guys

Well, if anyone here understands UPnP, you can help out.

I don't know anything about UPnP, I'll have to see how to do it…

@DimiDimit maybe you could look at this mod which does have UPnP Port forwarding:
https://www.curseforge.com/minecraft/mc-mods/mcwifipnp

That seems to be using WaifUPnP...

+1. UPnP is available on all the alternatives, but I prefer the settings of this particular mod a lot more. You could also look into adding support for using another LAN mod that has UPnP simply for the UPnP integration alone, while keeping this mod on top.