Found a temporary fix that, somehow, overcomes the problem:
1. right click the app shortcut properties
2. in Compatibility tab - check "run in 640X480 screen resolution" and click apply
3. run the app and let it open, then close,
4. Undo/uncheck (2) and apply, then relaunch app
I have to repeat the above each time I run the app. Had the same issue with previous winscp versions.
Running Windows 10 1903. Screen resolution: 1920X1200. Running a custom scale factor of %110 (to make everything a bit easier to see).