The most complicated game you've played?

I'm getting into Granblue Fantasy again and I'm amused by the insane amount of characters, summons, weapons and systems (though it's more likely to be called "hell").
What games did you play where learning all the systems would take a semester of classes?

• Granblue Fantasy - undisputed winner for me, 11 year old game where your team consists of MC + 5 party members, 10 weapons, 5 summons and 2 sub aura summons and many things locked exclusively behind hours of grind- now multiply that by 6 different elements! Wrap all of that up in a lightweight browser game and you lose the comfort many modern games have, you wll be navigating through a lot of visually outdated menus, but you can play it anywhere easily.
• Uma Musume - the core of the game is training the girls in a roguelike mode and then making a team of 15 characters for racing, training modes come in 10 different scenarios and there's a whole inheritance system for traits and skills, meaning a proper guide for the game could easily take 300 pages
• Arknights - Arknights has a huuuuge amount of gameplay content, collecting operators and learning their different skills and advantages takes a long time, then you can apply them to multiple different game modes and each event tends to have its own little stage gimmicks. Arknights is definitely the game where you need to use your brain during gameplay the most, but it doesn't have the kind of long running metagame like the previous two (which is probably a big plus for most players, you can start as a new player, raise 20 characters and be well covered for events)

I think what Arknights does is interesting, because you could pick a team of characters, be dropped into the game and spend hours just trying out different stages, you don't need to learn about every character or grind a ton of mats after having a team of useful favourites.

On the other hand, something with a meta game of building a strong teamcomp and gathering information on all these elements is fun in its own way- especially if you can't just throw money at the problem and pick 3 best characters from a tier list and be done with it.