I don’t use native myself but you should be able to use any C library you want so you should take a look at that.
Have you taken a look at the samples in the libui github repo? I don’t know of any others.
Are you just new to kotlin native and GUI or new to programming in general? In either case I would at least consider switching to kotlin jvm, since there are far more GUI libraries out there with much better documentation (libgui seems to be a small open source project with only a few people working on it).
Also if you are new to programming in general kotlin native might be a bit more complicated, because of memory managment, C interop and the fact that it is still in an early access stage.