There are no popular and new (like released in the last 2-3 years ... or maybe even more) MMOs. I see that people were counting on a couple of titles, or even stuff like Diablo 4 (which is hard to call MMORPG, but still), but everything died before release or was simply bad. Some older titles like WoW are alive because of that (and because they went free to play).
I have played Black Desert Online since its release. Right now, it's a bit disappointing for some people, but it is still really active, and updates are every week (with large content updates every few months). They improved many things over the years and it's still probably the best looking MMO. In short, PvE is good, PvP is disappointing (some may like it), there are a lot of AFK "activities" if you work and can't spend much time in the game. There were also many adjustments for new players to catch up (like literally, it's ridiculous how easy it's sometimes compared to how it was a few years ago) The game often has a "7 days free option", and if you reach some level in these 7 days (it takes a few hours) or something else (I don't remember what are requirements now) then you get it for free. I think there were promos on Steam, but there is a non-Steam installer, too (you have to register an account via the game's website, not Steam).
For me, it's like a single-player game, even though it's mostly an open-world MMO. I'm also ~90% AFK.
Check out Dosa, the master of swords and Do arts right now! – Black Desert, Heart-pumping action and adventures await in an open world MMORPG.
www.naeu.playblackdesert.com
All videos on the official website base on gameplay.
I'm not saying it's the best possible game, but I think I'm the only one who mentions it on OCF, so I guess most forum members don't even know it, and it's worth checking, at least, how it looks.