Is this restriction just for particular dates or days of the week, maybe?
After a recent flight change that had us arriving in Orlando a day earlier than expected, I priced out Disney hotels for the night of Sunday 2/20/22 (checking out on Monday, 2/21) a couple of weeks ago, and there were a dozen different onsite hotels with availability for that 1-night reservation.
We decided to extend our Universal hotel instead and didn't go with any of Disney's options, but after reading this thread, just now I repeated the search, and was able to go the whole way through the booking process for a 1-night room-only reservation (except that I didn't click to confirm the last step, as I don't really want the reservation) with no problem. I selected POFQ, but there were several others that were offered when I searched for just that one night.