macos – Hide conversations in Messages

I recently upgraded from High Sierra to Big Sur. Before the upgrade, each conversation in Messages had a little x I could click on to hide it.

I can’t find that option now, and Message is cluttered with lots of conversations I don’t really need to see.

There’s a “Delete Conversation” command, but the prompt makes me think that this deletes the conversation permanently. In some cases this is actually what I want (I don’t need all my old messages with verification codes), but in other cases I just want to hide conversations that are inactive, but not lose all the old messages completely.

Did they remove this option completely, or is there a hidden option to restore it?