I have exactly the same problem as described and still unresolved in https://community.rstudio.com/t/high-dpi-laptop-scrolling-too-fast-in-editor/31884 using an ACER ConceptD with built-in display under WIN10.
All possible adjustments offered in WIN10 settings have been put at lowest speed (which makes cursor movement and scrolling already a bit lazy on all other applications), but on RStudio it is still unchanged.
Q: Any ideas to slow down scrolling speed?