If you’re not sure which group the person is in that you want to mention, you can check for the group members at the top of the group screen. Finally, rename the group to something you’ll recognize next time or pin it to the top of the app. You can also change the color to customize it. These steps are catered for iPhones, but Macs have the same steps.
It isn’t necessary to enter “@” before typing their name using iMessage. Just type their name and the letters should become grey if they are in your contacts.
If the mentioned person has at least iOS 14, they can receive a notification for that conversation.
If you’re using a Mac and accessing iMessages via iCloud, you need to have macOS Big Sur.
To do this on an iPhone, swipe up from the bottom of your screen, then swipe up on the iMessage preview to force the app to close (if you have a Home button instead, double-tap that then swipe on iMessage to close it). Finally, launch iMessage again to see if the issue has been fixed. On a Mac, press Cmd + Option + Escape and select Messages. Finally, click Force Quit and re-open the app again.
