Well, for now you get my opinion until someone has more to say. This is Maerlande.
The list below contains many online forums which have been part of the Dominions community for many years. As some probably realize, online forums have taken a back seat to Discord but there are still great resources on many of them.
https://steamcommunity.com/app/722060/discussions/ This is the official forum for Dominions and the correct place to post bugs and the only place you may (if lucky) get a reply from Illwinter.
https://dom5wiki.gamelore.fun/ Dominions 5 Japanese Wiki
Possible additions that I do not have the information to create links. 4chan, Something Awful, maybe also the national communities (german, japanese, russian, italian, etc.
This tournament is intended to highlight short fast 1 versus 1 games which have unique strategies and tactics often different from typical multiplayer games with more than 2 players. If this interests you, drop by to learn more.
Main 1v1 bracket Dueling Tournament 2022
New Player Bracket New Player Dueling Tournament 2022
Join or discuss Dueling on Maer's Lande