Mona-Lisa Transeth replied
Hi!
Thank you, but as I said, it was impossible to change it (check the screenshot in the comment below).
I figured out how to fix it though, so I am putting it here in case someone else runs into the same issue and searches for the answer:
You need to click on the "Build query" button (which I would not have guessed in a million years), and there you will get a list of additional fields - including Post count, where you can change the number to whatever you want.