Sorry to bump this thread, but I just installed 5.1.7 and as far as I can tell WinSCP still doesn't manifest itself as DPI aware - on my high-DPI (150%) devices, it gets scaled by the system instead of being crisp, even though the linked bug is shown as resolved. Is there a bug tracking this work? Thanks.
Try the latest beta version:
https://winscp.net/eng/docs/history_old#5.2.4