Not OP, but I can say that it is a mode, which is its problem. You enter into the scroll mode and while not difficult per se to exit it can cause confusion. It is also pretty superfluous in the age of the touchpad and the ubiquity of the scroll wheel. Just another example of Microsoft working really hard to make Windows 11 look simpler, but not working on making it meaningfully simpler.
I don't know when middle-click scroll was introduced, but it definitely was before Windows 11, and at least as far back as 7.
Also, "no modes" is both a question of personal preference and a sliding scale. Input-has-focus is a mode, too, but getting rid of that would be an obvious mistake.
Middle-click scroll has been around as long as I can remember having middle-click. At least as far back as Windows XP.
Windows 95 had it.
Middle-click scroll was a feature of the Windows 3.1 drivers for a Logitech TrackMan I bought in 1994 or so.
Yeah, it's not a new thing, but an ancient thing, from the days of the button mice (a third button in the center---no scroll wheel).