Australia

I try MMOs but honestly the chat is full of cooker stuff and people raging. Minecraft servers are full of kiddies and I wouldn’t touch Roblox or Call of Duty with a ten foot pole (and I’m hoping Steam doesn’t get got).

If you're interested in multiplayer games with a more mature playerbase, may I recommend the Age of Empires franchise? With its most popular game having originally released in 1999, but being rereleased in an excellent remaster in 2019, plus a brand new entry in the franchise in 2021 and remasters of the other games having come in 2018, 2020, and 2024, you get the feel of playing a modern game, with an audience that is mostly more mature purely because they're older (or because they learn the community norms from people who are older).

That said, Minecraft is a very diverse game, and I'm sure there would be some corners of it that are more mature. I know there's an ongoing project to very faithfully recreate the entire Middle Earth, I assume that attracts a more mature type.

Just touching on the RPGs mentioned in another comment, if sitting up at the table is the problem, the prevalence of virtual tabletops and online TTRPGs these days may mitigate that concern. If you can sit at your computer for video games or social media, you can likely also sit at it for an RPG. Though focus may be its own issue still, I can't speak to your experience with that since it's so personal.