In this folder "C:\Users\WINUSER\Proton Drive\PROTONUSER\My files" that gets created by Proton Drive, a user should be able to include one or more Windows junctions (which point to folders elsewhere on the drive).

This would allow a user to set up a junction pointing to the same arbitrary folder XYZ on two or more computers, which would keep the contents synced between those computers and the Proton Drive.

(I have two computers on which I want to keep data in sync.)