I get warnings for my compose functions that it should start with a lowercase letter: This works fine in Android studio but for some reason not in IntelliJ. Is this a known issue or is there any configuration I need to make?

You need either Compose Multiplatform plugin from marketplace to get this and preview, or you can try a more sophisticated but unreleased custom built one here https://kotlinlang.slack.com/archives/C01D6HTPATV/p1659032360396019

That did it! shouldn't that one be installed or suggested if I start a new compose desktop project btw?