Okay you know what, I'd said earlier that I dont play any MMOs, but I forgot about one that MIGHT sorta be considered one, kinda, maybe, so I may as well offer it as a suggestion.
Path of Exile 2. If you've ever played Diablo or a game like that, it's quite similar in base concept... there's a very heavy focus on getting exciting loot (mostly equipment) after clobbering like 10 billionty monsters, and coming up with character builds and whatnot... it reminds me in some ways of certain things back from my MMO days... as MMOs often quickly become a search for all sorts of items and such, like everyone wants the... er... like the baseball hat of destiny or whatever, I dunno. Super focused on that concept, while fighting huge hordes of monsters. If you've never played a Diablo style game before, definitely check them out, I tend to think there's a heavy overlap between people who like MMOs and people who like Diablo-style games.
But the one huge difference is that you're not always in a single continuous shared world. In PoE 2 specifically, when you're in any of the town or hub areas, you'll see other players wandering and doing whatever. When you leave to enter any action zone, that zone will generate for you as an instanced area. So, only you and those you personally invite will be in that specific instance of that zone. During gameplay you might pop back to town (using a portal, which you can generate at any time) to sell or stash items and then pop back to that separate instance, where you and/or your group will be sealed there again, nobody else able to get in.
Note that this does not prevent others from accessing a given place. You're not going to go find like, the Castle of Screaming Doom or whatever and be like "oh geez, it's already occupied". There's no limit on zone instances, so there's never an "I cant get in, I have to wait" moment. Some actual MMOs do this (I remember City of Heroes did, sometimes) and others dont do it at all.
There is no PvP in a game like this, only PvE.... the purpose is to find gear and power up, not find gear and punch each other. There are things like leaderboards for each season though, if you're into that kind of thing, but that's absolutely not necessary.
It's an action-based game, you arent going to stand in front of a single enemy and rotate through a skill bar like in many traditional MMOs. You do have a skill bar, but you'll be dodge rolling and comboing skills and all this stuff, mostly there will be many enemies at a time instead of just one or two. You dont have to be a master at it or something, but it is not an easy game, you can expect to die sometimes. The combat is so freaking good though. The bosses in particular are spectacularly designed. Just amazing.
The game's downside... or upside, depending on how you look at it... is that it's got a very harsh learning curve.
Like, look at this:
That's the passive skill tree. When you level up, you pick a node and activate it. You start at one of the six nodes connected to the character portrait (which one you start at depends on starting class, but there are no class restrictions on nodes or where you can go on the tree), and you spread out from there. Every individual one of those little things is a node and every one of them does something. The game is famous for this bonkers skill tree.
Oddly, it's not as hard to navigate as it might look. Nodes are arranged in all sorts of shapes, and those shapes generally hint at what that group of nodes is about. Like that one at the bottom right edge, it looks like a spear, it is entirely full of nodes that are best used with spears. An arrangement that looks like a flame is likely full of fire-themed nodes.
I went into this game just refusing to use any sort of player-written guide (as I wouldnt have any fun if someone else made the build for me) and I've honestly not had any trouble dealing with the tree. There's even a search function, so if you're like "geez I need some lightning resistance" you can just type that and nodes with that will light up.
Much better than the first game, where the tree looked like this perfectly symmetrical blob, I remember trying that and I just couldnt deal with it, it just all looked the same everywhere. But this? I can do this, I think it's pretty great.
There's a lot of other mechanics in place too, like the game's "crafting", which doesnt work like that concept in other games. Unlike a lot of MMOs, your gear is not static, and all sorts of things can be applied to it to alter it and improve it. Or totally ruin it, if you make the wrong choices. You have A LOT of freedom in how you build your character. But there's a heck of a lot to learn.
It's a freaking gigantic game with so very much content, and a lot of different mechanics interacting. I found that the game does a good job introducing them to you over the course of the campaign. I have yet to hit a point of being like "argh I dont understand this". But you gotta be ready to read and think about stuff.
There's a lot of like, tutorials and such on Youtube and whatnot, but I cant really speak for them as I didnt really watch any, since I havent gotten stuck.
Seriously the game is so, so good. I dont know how it plays with a group, but I know a lot of people love playing it that way. Others might play the actual combat sections solo, but maybe trade items and such with players in towns. Others like myself just do absolutely everything without help. As far as I know, it's great regardless of how you go about it.
I'm not really much for grouping and whatnot, but if you were to decide to try the game, what I can do is answer any questions or give advice and such as you go. I dont handle super direct conversations well, but I can absolutely handle conversation over the internet. Through text, I mean. I dont do voice chat.
Anyway, yeah, that's my suggestion.
Be warned though, the game takes up a lot of space. 120 GB, last I checked. Also as this is an online game in very active development, changes and additions come sometimes. Though, if you're used to MMOs, chances are you're familiar with that part.
If you want to try this one, you'll need Steam. Though, if you intend on doing much PC gaming, you'll want Steam just in general. That's THE place to go for PC gaming.
There is a console version too, on the Xbox Series Whatever. I havent tried that version though.
I'm actually going to install it on my new Steam Deck, see how it goes there, the site says it should run well on that. My actual main PC is like out of space, so I havent played it in like the last couple of months. Turns out, 1 terabyte is not enough for all the stuff I do.
Sorry, that was very long, I dont mean to be overloading anyone with it. But I get enthusiastic about stuff like this.