Does anyone directly reuse Compose code between Android and Desktop, or do most people write this code separately (one platform only)?

I would hope they write the code to be shared via Kotlin MPP as demonstrated here: https://github.com/JetBrains/compose-jb/tree/master/examples/imageviewer

Probably in terms of sharing code between Android/Desktop todoapp or issues will be a better example

Yeah it's reusable, I'm sharing 98% of the code in one my open source library which is in very early stage, that's why it's private for now But as shared above those are some really great example of shared code between Desktop and Android