I don’t even play Crusader Kings 3, but this is exciting! And geeky!
Basically, a mod team created an opportunity to follow Ireland’s mythic history (which might possibly have some connection to actual prehistory, but nobody knows what it is), in which many human groups with magical powers invade Ireland, until it finally sticks. And you get to attempt to conquer Ireland over the course of all that mythic history, as the leader of one of these invasive factions.
Now, in the actual Lebor Gabala Erenn, most of the settler groups all died tragically, but not in this game! Nope, they are still around and kicking.
The other trick is that, possibly, some of the invader names actually refer to various Celtic groups and their influence on Irish history. One of the most suspicious ones is the Fir Bolg, because maaaaaybe they refer to the Belgae, a Celtic tribe that managed to go everywhere you want to be. Including some expeditions to Greece. Others point to Pictish stuff.
So anyway… the Crusader Kings 3 mod is called Tales of Ireland, and it really looks beautiful.
OTOH, they did change a lot of stuff for game balance, and they went in for a lot of “de-Christianization” that seems to go way way way too far. (When you decide to have monastic round towers turn into some kind of Paleolithic or Bronze Age structures built by the Nemedians, you’ve definitely gone too far.) They also decided to add “the Celts” as a separate faction, when (as the video points out) the Children of Mil are the Celts, possibly with separate Celtic helpings among the Fir Bolg.
OTOH, a lot of this is for the sake of humor or fairy tale situations — if you hang around the Giants’ Causeway, you meet up with giants, not with basalt oceanic rock formations.
Anyway, it seems pretty full of flavor and interest.