Hi @ashimabdul ,
Are you using Power Automate (MS Flow) to post messages to a Teams Channel with HTML tags?
Could you please share more details about your Flow? Which connector are you applying on it?
I made a test on my side, create a Flow using “Post a message (V3)” connector, contents with HTML tags, and it worked fine:


As you seen, message posted in bold correctly. If you are using the same connector, you could remove and re-apply the Flow on your app.
Please have a try and hope this help.
Best regards,
Community Support Team _ Jeffer Ni
If this post helps, then please consider Accept it as the solution to help the other members find it.