Most commonly called a 'skill ceiling' in video games. It's not exactly the same as complexity though.
Some games are complex in the sense that it's computationally difficult to 'solve' them perfectly, but in terms of human splaying the game, a few simple heuristics are good enough to make the game quite boring. And the inverse of this: even if a game can be solved by a computer, the game could have an essentially infinite skill ceiling for humans and they will never run out of non obvious situations, because humans can't rely on the search speed through the game states as the computer.
A classic board game like Agricola has a pretty insane skill ceiling, though it looks fairly simple on the surface.
Many board games with a strong multiplayer element necessarily have a high ceiling. Once the players discover a clearly 'best' strategy, they will play to deny this strategy from their opponents. In a role-selection card game, you might pick a key card to an opponents build from going exponential, even though you don't need the card yourself. Or if a class of cards is overpowered, simply having multiple players fight over those cards makes that class of cards less powerful.
Just having freeform trading does the same. Monopoly is a classic example of a legendarily terrible board game for numerous reasons. But simply because it's a game involved trading and negotiation between players - that's a huge open field for skill to enter the game. (I absolutely do not endorse playing Monopoly, there are far better board games that do similar things.)
Got into chess this year. One disadvantage of chess and other games in the perfect information category like go, is that they are too engaging for me as more thinking feels always worth it. I need to actively stop myself from playing all the time.
Pure curiosity
I recently realized why sometimes I find board games/puzzles boring after a while:
The returns on "cognition" for these games has a sharp cutoff. While this seems a bit obvious in retrospect, I haven't seen anyone talk about "returns on cognition" in any other context apart from thinking about AI-Doom scenarios.
One thing that always made me a bit frustrated with different board games is that a lot of them get relatively boring once you've played a few times, and there are a lot of heuristics that are obviously close to optimal play. Other games really encourage me to "actually think", because there are highly non-obvious situations coming up all the time.
One example for a game that is boring, once you have figured out you always need to put the big numbers in the corner, is 2048. But there is a close cousin of this game Dive where you can merge the numbers if they are multiples of each other. For Dive I don't have any good heuristics like this, and it feels more engaging for that reason.
Interesting concept I stumbled upon while googling: