User blog comment:MisterWoodhouse/The first migrations to the Unified Community Platform/@comment-43838113-20201003105840/@comment-47011541-20201004013128

It mainly depends on what’s been said in various other update posts:

Removed features: Chat, Forums (thread-based), WikiActivity (there is a script available to have it restored)

Unknown - Welcome tool, Message Wall Greetings (you could use this script to restore it), WAM scores

Anything I didn’t mention has an unknown status for UCP transitions.