What are the differences between these two choices in G Suite Gmail's Interface?
It seems Gmail calls it "Conversations" in the UI (at least in Gmail), but "Group Messages" in support.
Once acknowledging this limitation, the answer is in About rooms and group messages, which states:
- Conversations are basically 100% identical to a regular chats except having more than 2 participants.
- Rooms offer features such as:
- Setting a room's name
- Entrance moderation
- Assigning tasks
- viewing shared files