@shodanx2 ,
Placing the cursor anywhere on the window and middle-click-dragging left and right
Interesting. Apparently I am not creative enough to think of clicking on anything but the window/subwindow/panel frame to try to resize a window/subwindow/panel. Since there’s apparently utilities to enable that in other things, I guess you’re not the only one, but it’s just not something I’d ever thought of. (And sorry, in case it wasn’t obvious, unlike @Alan-Kilborn , I didn’t originally understand that you weren’t just trying a different button on the center bar between.)
Which allows me to middle click drag anywhere on a page and very quickly scroll it up and down.
That sounds very much like browser-style autoscroll features (though in those, they just click-and-release on the middle button, and that switches to autoscroll mode). And autoscroll as a feature has been rejected time after time after time(*) after time after time after time(*) (where the two *-d times were official word from the developer saying that autoscroll won’t be implemented). So while people obviously like it, the developer has made it clear it won’t be native to Notepad++.
So a script (as @Alan-Kilborn has given you hints on) or writing a plugin are the only options for your autoscroll-like behavior.
Regarding the script – if you search the forum for PythonScript and the mouse-based messages, I am guessing you’ll find an ancient script by one of the regulars here who gives an example of intercepting the mouse actions to add features to a script.