In CC 2018 version 19.1 and Windows 10 Adobe fixes the windows UI scaling Problems ant it became automating and uses the Windows scaling for each of your displays. For older windows 10 version and older windows version. The are issues in Photoshop Windows UI scaling the Photoshop UI Preference may have meaning on machine running old windows versions, and the setting may be global for all displays not just high ppi resolution displays attached to you system. The settings is automatic on newer Windows 10 versions.
Forcing Windows displays scaling onto Photoshop will scale not only Photoshop UI it will also scale the image Photoshop displays. A registry Update is not required for this on windows 10 you can do that in a Windows 10 start up shortcut that starts Photoshop.