It is not clear from your code example which object is leaking and how you detected it. From a KMM user's perspective, I would suggest keeping all logic inside KMM, exposing only simple functions... and not creating reference cycles like KMM object -> Swift object > KMM object - these cannot be properly resolved, neither by garbage collector nor by ARC.
Also, it looks like it's not Compose Multiplatform issue, so it's better to make very small project that reproduces you issue and either ask it in #C9JM6Q2UX / #C3PQML5NU channel of file an issue in our YouTrack.