Wish is the highest level spell in the game. There are predefined things it can do, but because of the open nature of tabletop, it can do just about anything, as long as your Dungeon Master approves it. The spell doesn't exist in Baldur's Gate 3 for the players, since it would completely break any encounter, and because players can't merely tell a computer what creative thing they want to do with it. Also, we never achieve the level requirement to cast Wish in Baldur's Gate. As far as the mechanic behind Vlaakith's usage, they coded it to outright kill you. No rolls to see if you evade, no possibility of response, just poosh! Dead. It's the only time you'll see the spell in the game and you don't know that's what happened at the time.

Edit: if you enjoy fantasy, board games, and adventure, then you should definitely check out D&D! They sell starter packs for $20 that have everything you'd need to play an adventure with a group of friends. D&D 6e, or One D&D as they're calling it is coming out later this year, but I'd stick with 5e, which is the game everyone knows and loves. Hasbro bought Wizards of the Coast a while ago, and they've been displaying typical big corp malarkey and greed. Avoid anything new from them and stick with what is familiar in my opinion.