The @mention functionality is not consistent.
When a user is @mentioned in a Comment, they receive an email notification (if setup).
However, if they are mentioned in a chat, they do not. AND, @mentions do not even work outside of Comments or Chats.
When a user is @mentioned in a chat, they are currently not receiving any notifications - email, mobile push, or Slack.
Use Case
Given a user is @mentioned in a chat and they are not actively on the board (or at least the chat windows is not open?) at the time of the @mention, then a notification would be sent to the @mentioned user, e.g., similar to @mentions in Comments.
Here is the Got a question? post that sparked this Wish List post:
https://community.miro.com/got-a-question-ask-the-community-45/atmention-notifications-in-chat-1641
Some links to current documentation regarding @mentions in chats
This @Mentioning People on the Board help article is misleading, specifically where it states, ‘you may need to quickly notify someone about the changes you’re making. You can do that by simply @mentioning them in a comment or chat.’ I have tested this and no notifications are sent.
Further review led me to this article, which more accurately describes the actual behavior:
The Chat help article that is linked to from the @Mentioning People on the Board article does do a better job at explaining the current, intended behavior: