As you can hopefully see, the content of the binder is not taking up the full space. This has happened about two times on my new Mac. I was on Windows before and I don’t remember whether this happened.
The first time, closing and re-opening Scrivener fixed it. But this didn’t work the second time (yesterday). Today it was fine again. The only thing I can think of right now that changed was that the machine had been sleeping and some time had passed.
I also don’t know how to make it happen on purpose.