Hello!
Did you happen to follow the steps others have posted by clicking the microphone on the bottom?
If no microphone I did make a comment earlier:
If you don’t see the microphone icon on the bottom right, go to Settings > General > Keyboard and turn on “Enable Dictation”. In fact just turning on Dictation alone may get rid of the red audio symbol.
I believe it’s just a new feature/function, you can see it referenced in this article:
Send and receive audio messages on iPhone - Apple Support
If you’re still having troubles, let me know, or anyone else here, the results of those steps, glad to help if I can!