I've just installed OpenTTD 1.9.1 in Windows 10 and got surprised that the game does not scale according to "Scale and layout" settings of the display. I usually play in window mode (not full-screen mode) with scaling set to 175% because of high resolution of my display. And I was really sad that now the game is unplayable for me, because its window was displayed without scaling. I dig a bit and found the following issue on GitHub, with solution to my problem:
github.com/OpenTTD/OpenTTD/issues/7468
Summary:
1. It seems that there was a DPI-aware change in source code (
255fa6e
) which disabled Windows' scaling in 1.9.0 - see PeterN response in GitHub.
2. Solution: change application compatibility settings as shown on picture
here
-see nielsmh response.
It works!
I hope somebody else finds this info useful

Happy gaming!