Kotlin Multiplatform gives the mechanics to compile code to different platforms/targets. So it can compile code to Android, native iOS/linux/windows, web, beta web assembly, java runtimes and more.

Compose Multiplatform is the Flutter equivalent. They work on a UI toolkit which compiles to desktop/mobile/web. It works with declarative patterns like Flutter/SwiftUI/React, so is a quite modern implementation to build UIs. So it is possible to build desktop apps. Jetbrains have build their toolbox app as first desktop app since a few years using Compose. It provides many UI elements to build Desktop apps and as Jetbrains itself is a big Desktop app developer, you can expect they put their expertise into it to make it as good as possible.