After 2020 Wave 2, Real Time Marketing and other features were added to the full marking solution. These features still don't appear in the 'Solution Only' install/environments.

Even if they are non-functional, the 'Solution Only' solution should at least have enough of the entities and metadata to provide parity with the full solution. Otherwise, hard to migrate between solutions due to missing dependencies.

I mean how would I develop a customization for real-time marketing in a solution-only environment?