Sorry this is not feasible yet. The only way to do @ mentions is by using the full Bot Framework APIs.
There is a feature request for this issue: https://microsoftteams.uservoice.com/forums/555103-public/suggestions/17153099-webhook-needs-to-support-forced-notification-a-la
Please upvote it.
Teams Incomming Webhook Mention
AK
26
Reputation points
How can I mention when I POST to Teams Incoming Webhook in json format?
(For example, if you enter "title" for the title and "text" for the body, it will be reflected in the Teams post.)
Accepted answer
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Prasad-MSFT 8,506 Reputation points Microsoft Vendor
2021-08-10T04:26:03.89+00:00