When it was introduced, I was skeptical about Stage Manager. I always thought that a classical window management system wouldn't work on a touch-based device, but I have confidence in Apple when it comes to this sort of stuff. In the end, it's been a failure.
Some people argued that this shows Apple should implement a macOS-like interface, or even macOS directly. This doesn't make any sense. Apple has adapted windows in SM so that controls (resize handle, top bar...) have the precision of a fingertip, and that they replicate the metaphors we're used to in touch-first devices (for example, dragging instead of tapping). Even then, the experience sucks.
So imagine how bad a macOS-like interface, with traffic light buttons, infinite resize and positions, etc. would be. Well, we don't even have to imagine: we have dozens of Windows 10/11 so-called tablets out there, and no one* use them as tablets.
In the end, I think the professional potential of the iPad goes in line with maximizing the iPad-like, single-window interface. There are tons of AR, illustration, video editing, etc. apps. Customers use them professionally. Some people think making the iPad a professional device means making it a subpar PC. No professional user would buy that.