BG3 is based on arguably the most user-friendly version of Dungeons and Dragons, 5th Edition (5e). Larian themselves also do a fantastic job at easing you into the mechanics via gameplay, so you can honestly jump in and just play something that sounds cool to you without worrying about having to min-max or optimize your character. The game lays out what you get on each level-up pretty well and it defaults you to being a single class, so you won’t have to worry about multi-classing unless you want to - and because it’s based on 5e, you can honestly get away with not optimizing your build that much, if even at all, and manage to do fine as long as your main damage (STR for melee, DEX for ranged and Finesse weapons)/casting stat (INT for Wizards, CHA for Bards/Sorcerers, and WIS for Clerics/Druids) is high.
Can’t speak on OW2, but with games like Deep Rock Galactic and Vermintide, I found it’s best to just play it and figure stuff out slowly from experience. A lot of it can sound complicated, but I found it’s easier to digest the complexity of the mechanics and systems a bit at a time as your experience with the game grows. Like with Vermintide, as an example, I recently started really diving in deep with Cleave, Stagger, and Frontline/Heavy Frontline/Tank property mechanics and numbers for melee weapons; you literally cannot see these things from the game’s UI, and starting out I had no idea these things even existed, and it only really matters once you start playing on the hardest difficulties, Legend and Cataclysm. If I had to figure out all that stuff early on, I would nope out of the game super quick lmao.