https://wccftech.com/imessage-will-get-mentions-and-undo-send-in-ios-14-and-macos-10-16/

Apple is working on implementing new features in iMessage such as mentions and undo send. The features are currently under development and could be released as part of iOS 14 and macOS 10.16 operating system updates.

As per MacRumors, Apple is finally working on bringing mentions to iMessage. This would allow users to tag anyone in a direct, or group conversation, using the @username format. This mention format was made popular by Twitter and later copied by Facebook. Slack, Skype, Messenger, WhatsApp and every other popular messaging service provide support for this mention format now. This allows users to get the attention of a user by mentioning them. It also allows users to only be notified when they are mentioned in a group, rather than receive alerts for each message in a group chat.