So I prepared a model publish and associated image posts and I was trying to schedule them to publish on the 1st of December. However I could not switch to December on the calender card (see screenshot below).
After trying a bit back and forth, I found that my "problem" was viewing my browser window in full screen mode. I had to go to partial view mode and shrink the height of the window until a slider appeard on the right of the scheduler. Like this I could scroll down and change the month (see screenshot below).
Before doing so, there was no slider present and the month selection was hidden by the top of the browser window.
Initially I wanted to post this as question and a call for help, but since I figured out a "solution" myself, maybe this is helpful for somebody else.
I am using firefox browser on Windows 11, but I don't know, if this has something to do with the browser.
EDIT: I just noticed you can also zoom out (press Ctrl and - ) to see the month selection.