As always with Jira, there's a feature request for that that's gathering dust for several years. Needless to say, this is vital for the Teams notification to be of any use.

This would be extremely helpful to our workflows.  
Its a huge gap in functionality that really prevents us from doing more with the product.

FYI, Mentions are now supported in webhooks by MS:
https://learn.microsoft.com/en-us/microsoftteams/platform/task-modules-and-cards/cards/cards-format?tabs=adaptive-md%2Cconnector-html#user-mention-in-incoming-webhook-with-adaptive-cards

[EDIT]

Just realised the post I saw was from 2021!

+1 this feature will be very helpful

+1 Definitely worth incorporating. I can understand the delay if you'd have to re-architect the approach to Teams, what with all the changes to Graph API etc. lately.

+1 really necessary functionality. At least in Slack you can mention a whole channel or individuals if needed, and in that app you can customise your own notifications so you're notified of a specific phrase. In teams you can't do that, so not being able to notify a whole channel of a specific action or alert is really limiting

I have a team member who fails to use email but will check an @mention in Teams. With Webhooks, I can send a message when he's assigned to an issue, but it won't @mention him so it doesn't really improve the likelihood he'd respond any quicker.

+1 and +100 for it being able to open a chat with ONLY the reporter and not a channel

+1 Vote for this improvement

+1 would be great