This is what I see when I long held the calendar icon and also when I went to the calendar settings under alerts
Apologies if I'm off-base here, but those screenshots are when you go to the
Settings>Apps menu, then select Calendar. The screenshot I shared previously is when I go to
Settings>Lock screen. Can you show us a screenshot of that?
I can reproduce what you're seeing in the
Settings>Apps menu if I toggle on the Hide Content switch in the
Settings>Lock screen menu. If that toggle is on, then when I go to
Settings>Apps, select Calendar then tap General Notifications, I only get Hide Content and Don't Show Notifications when I select Lock Screen on that menu. If the Hide Content switch is toggled off, then Show Details becomes an option.