@channel notification does not work from Microsoft Flow integration
When you type "@channel" into Teams, it replaces your text with an object that represents the channel.
Unfortunately, when using "@channel" through the Microsoft Flow Post Message, it just leaves the text "@channel" and doesn't notify members of the channel.
Slack has a similar feature but leaves your text as text, and triggers off of that. I believe this should work similarly. @channel or other notifications should trigger regardless of source.