The Trash folder shows how many messages are inside and counts down the days until they're gone for good.
You can restore entire chats or just pick the ones you want, and any new messages from trashed threads pop back into your Inbox.
Want more control? You can tweak swipe gestures for easier access under Settings > Swipe actions.
Just note: deleting single messages from a chat won't send them to Trash—it only works for whole conversations.

These updates are rolling out gradually, so not everyone will see them right away, even if you've got the beta app.
These updates appear in Google Messages for Android and finally add a way to recover lost chats, which was missing before.
The update adds Mentions for RCS group chats and a Trash folder for recovering deleted conversations.