you can work with tags in your Team, there is an action in Power Automate to get the @ mention of a tag from a team. In this tag you can add multiple people that should get a notification.
The standard mention is done by <at>[User UPN]</at> as an HTML when sending a message to a MS Teams team. This does not work with mentioning the whole channel, probably because some more information are missing, like the actual "mentioned" information. This is maybe not implemented (yet, please consider this as an idea in this forum).