Using Proton Calendar is like 75% a good experience, but the reason it doesn't go all the way is all around how calendar invites work. 

Sometimes it will pick up that I have an invite in my inbox, but sometimes it won't or I won't be sure whether it picked up an update to a change in the event. Even with that I think it sometimes works, but because of this janky feeling workflow I end up double checking in a way I don't do on Teams.