I'm not super up to date but if you're willing to look at older games with active modding communities, the Elder scrolls, Fallout, and Stalker series' stand out

I'm not super up to date but if you're willing to look at older games with active modding communities, the Elder scrolls, Fallout, and Stalker series' stand out as having very active modding communities. ModDB is also a great resource (was, not sure if still the best), you can figure out where the crowds are at based on levels of submission and discussion activity there. PS Minecraft modding is an interesting example of where those commercial revenue-focused practices have bled into the modding scene. Never have I seen so much adfly, patreon, and general money-making motivation within a modding community. I doubt it's the only one that suffers from the issue, but it's notable.