I've noticed the same thing. What's weird is it does not happen to all Teams invites. I have some that have the join button, or at least show in the "notes" area a Join Meeting URL, which I can click. But others have a blank "Notes" area. And I can't find anywhere the link to join. If you save the calendar event as a .ics file and open that in a text editor, I can see the URL for joining is there (although copying it and pasting it to a browser does not work). The only way for me to join, is to open the .ics file in a text editor and copy the meeting ID and password, and join teams using the meeting id and password. Frustrating and annoying as this causes me to be late to my Microsoft Teams meetings.