Very likely started thermal throttling because apple is notorious for not putting adequate cooling on their mac books. This game uses fluid dynamics calculated

Very likely started thermal throttling because apple is notorious for not putting adequate cooling on their mac books. This game uses fluid dynamics calculated in real time, i don't think its designed to be super optimized but rather super true to physics. Most of the time game optimization involves cheaping some of the complex calculations to be less accurate but still "good enough" see https://en.wikipedia.org/wiki/Fast_inverse_square_root https://en.wikipedia.org/wiki/Fast_inverse_square_root for an example. In other words you'll run into this issue any time you do anything taxing for more than 10 minutes on a mac book.