
If you want to mention someone in a Teams chat or channel message from a Flow, the key is to use the “Get an @mention token for a user” action first. This action generates a token that you can then include in the message body of your Teams post so that the user actually gets tagged/mentioned.
This steps for mention user in chat
#1. Add the Get an @mention token for a user action in your flow.
#2. Specify the user (by user principal name or user ID).
#3. Use the output token from this action (usually something like @mention) inside your Post a message (in a chat or channel) action.
#4. When the flow runs, Teams will render that token as a real mention so the user gets notified.
Note: This action only returns a mention token for users right now, there isn’t an out‑of‑the‑box action for team or channel mentions in the same way yet, so for those you'd need to call the Graph API.
Reference Link:
How to mention User: https://learn.microsoft.com/en-us/power-automate/teams/send-a-message-in-teams#mention-a-user-in-any-message
How to mention Team or Channel:
https://damobird365.com/mention-a-channel-or-team-power-automate/