Well there's Age of Mythology, which had a definitive edition announced a couple of years ago, and which just today they made an announcement of an announcement (don't you love that those seem to be a thing now...) of more information coming up next month.

There's a new Company of Heroes game that came out last year, and a shockingly high-quality open-source RTS called Beyond All Reason, and an RTS-ish Dune game from 2022. None of these really appeal to me though, as I just love the gameplay style of the Age franchise. So I don't really know how strong they're going.

Last year also saw the release of the finished version of the massive Battle for Middle Earth 2 mod Age of the Ring. That's a game that you can't even buy any more, from anywhere, and it still has enough of a community to support that interest. (Admittedly, personally I would include BFME in the "rts games are all dead" category, but perhaps it's just not quite as dead as one would think.)