Weird. I just went to the shorts page now and it says what I described.

I just tried on Chrome and Firefox on desktop, and the iOS YouTube app. Both show me a message saying "Recommendations are off. Your watch history is off, and we rely on watch history to tailor your Shorts feed. You can change your setting at any time, or try searching for Shorts instead."

I'll also clarify, sometimes if you click on a shorts video that you searched for manually, a few related videos will be queued, but then the feed will try up and the watch history message will display again.

Do you have left over watch history from years ago you've never cleared, and maybe shorts is enabled since it uses that...?