I did/ would do the following order:
• Logic/viewmodels to multiplatform with expect/actual implemtation for platform specific things
• Implementing a start point for the iOS app
• Thinking about resource management/testing it on iOS (multi language, images etc)
• Migration navigation in your android app to either a custom one that works with multiplatform
• Start Migrating all Android compose dependencies to múltipla dependencies and check where you need to change code
• And then you can finally move your compose code to a shared module