cookie clicker. i play it online online because i "play" it on the browser. perfect for second monitor and mindless. you don't have to deal with any people whatsoever.

you can also try old school runescape (that's actually online). it's basically the de facto second monitor game. there's lots of grindy stuff that is just relaxing to do, alongside good quests and hard challenges with regular content updates chosen by the community. im on a break though because i don't have a second monitor

Guild wars 2and FFXIV, although they aren't really second monitor material I think.

I still log in to Elder Scrolls Online every day to check how my stuff is selling through the guild trader, I'm missing a few rare companion armor pieces and they're all expensive. There's also an ESO expansion coming out in 2 or 3 weeks which will add new customized skills so I'll check those out for sure.

Also started Star Trek: Resurgence since it's on Steam now, it's a single player telltale style game though, liking the story so far. It's written in the 90s trek style.