Hey man,
with all the respect, that's not the lack of functionality, That's BS from Microsoft. I don't think they don't know what they are doing.. Win 10 calendar worked on all screens and was pretty convenient, now they screwed that completely in Win11. It's very poorly arranged and limited just to main screen, they know it so they should fix it if they care, which does not seems like.
If they did any testing in the Win 11 system they have to be aware, so rather looks like they do it on purpose to be able to say , 'hey we upgraded calendar in win 12' ... :D
People forgot that MS said that Win 10 is last system version and they will just do plugin and upgrades on that onwe, then they realized they would be screwed in sales manner, so released Win 11 piece of sheet silently.. I would be very surprised if they would do any (positive) change to this part of the system until win 12 or later release :D
BR,
Martin