Shouldn't the "Switch to the calendar tab" open a new tab containing the calendar,

It does here. Try a new profile and see whether it works there.

Let me add to this issue that doesn't look like it was resolved at all. And yes -- I would agree -- this is a bug of some sort. For one, I don't even HAVE the ability to customize my menu bar to "switch to the calendar view". The only way I can do that is from the Events & Task menu. When I select Calendar from that menu, the Calendar is all I can see. The only way I can get back to my mail is by viewing something else, like Options. At that point, Options is rendered in a tab along with Calendar and Mail. If I make the mistake of closing Options first ..the Mail tab goes away and Calendar is no longer a tab but the whole thing again. To get mail back, i must go thru the dance of opening the options tab again to get the mail tab back and then make sure shift the focus to my mail tab before closing the options and calendar tabs. This is utterly nuts. I don't remember exactly when this behavior began to exhibit itself.

Also .. I run Thunderbird on two machines .. the exact same version (68.7.0 32 bit) but one where the menu uses different -- UK? - spelling (Favourite Folder vice Favorite Folder and Deleted vice Trash). The one using "Favourite" rather than "Favorite" doesn't have the calendar tab view issue .. the one that uses "Favorite" does. Makes me wonder if there might be something in the calendar settings causing this issue. It's really annoying. And I'm surprised that an issue reported 5 months ago is still hanging around after quite a few updates. Thanks!

charwing,

please start a new topic for your problem. https://support.mozilla.org/questions/new