Speech recognition in Teams is still under development. In fact, there have been reports that even muting a Teams call still doesn’t allow one to use Microsoft Speech recognition to operate without exiting Teams entirely.
I was in my Teams staff meeting and needed to type several sentences into Teams. I decided to try a modest hack. Without even muting our conversation in the Teams video conference, I opened up Microsoft Word and hit the Dictate button to dictate those sentences into Word, fully expecting a failure or error message of some sort. But, no, Microsoft Word recognized every word correctly. Then I could copy and paste into Teams. Since then I have tried it several times and it always worked. Until Teams has native speech recognition, this is an easy and simple workaround.