I while back (I think in June 2023) I had made a list of issues while we were still evaluating KMP (and specifically K/JS).
One of those issues was
https://youtrack.jetbrains.com/issue/IDEA-300618, which made the transition for Java developers a lot more cumbersome (as the strategy was to compile to the JVM target first).
I've just seen this PR
https://github.com/Kotlin/kotlinx.coroutines/pull/3987, which AFAIU is the foundation for IDEA's debugger enhancements.
Looks like finally we'll be able to step over and in coroutines code correctly.