Forum Discussion
Create Workflow mail to @mentioned user in discussion boards
How to send notification mail to @ mentioned users in SharePoint online discussion board
Discussion Board List in SharePoint site
are you getting the suggestions to appear:
In my case the suggestions came up. When hovering over the suggested names SharePoint gave me the email address from the user in a tool tip and I received a notification on that email address.
Yes i got this i can @ mention users but they dont get notification
You might want to log a ticket for this with MS. as the base functionality does seem to be in place Maybe something wrong with your tenant.
or we can do a workflow