Yes you can get a 7/7 score for a combinatorics problem in IMO with a good amount of handwaving e.g. instead of formally describing a configuration of monsters in P5 of IMO 2024 you can get away with a few sentences that describes what you're doing. There's actually a decent amount of compression being done by using informal language, so I expect formal proofs of combinatorics problems to be significantly longer than formal proofs of algebra/number theory/geometry problems.

I should say that handwaving is also ok in other topics, but formalizing handwaving in other topics is easier.