Mail 15.0 Send button disabled!
Mail 15.0 (Monterey 12.2.1): the Send button is disabled in most new sending windows such as a Reply window.
A minor complaint is that button icons in all(?) new sending windows are also disabled, showing text only.
A workaround is to hit the Attach button then cancel the consequent Attach dialogue. This re-enables the Send button.
I hope Apple fixes this quickly: it's really annoying!
MacBook Pro with Touch Bar