I installed the desktop version of Draw.io on my Ubuntu system using the Ubuntu Store (snap). When trying to save files to my Windows partition (or mounted device other than / (root), a received the following error:
After some digging, I found that the permission for the snap defaulted external devices as disallowed.
Had to simply enable “Read/write files on removable storage devices”, and viola!
Hope this helps other seeing the same behave from this or other snaps.
Cheers!
