Insta chat flag?

The orange flag in the Instagram DMs is a tool designed to help users manage their messages more effectively. If you see the orange flag or triangle in your DMs, this means that the respective chat has been marked as important.

This feature allows users to mark certain chats that they want to keep in mind or follow later. Once a chat is marked, it is easier to find in the DM input, so users no longer need to scroll through numerous messages to find a certain conversation.

English from OwskiMedia.co.uk