I have a Microsoft Surface Book 3 & Surface pen. Adobe DC used to automatically recognise my pen for markup, and I used my finger to scroll.
about 3-6 months ago, I lost this ability. (yes, "Auto detect pen hardware to enable markup" is ticked in preferences)

At the moment, the pen only works like a second mouse.

So far, I have removed and re-installed Adobe. Auto pen detection did work for 1 PDF but stopped working again.
I've also re-installed the pen drivers, but this has not helped.

Auto detect pen for markup works perfectly okay in Microsoft Apps like whiteboard, OneNote, Excel etc.