If you have Window 10 Creators edition and CC 2018 19.1 the UI scale Preference does nothing it not used. It is your Windows Display settngs.... set it to 100%
Windows High-Density Monitor Support
With this release, Photoshop on Windows 10 Creator’s Edition now offers a full range of choices for UI scale factors from 100% through 400%, in 25% increments. This means that the Photoshop user interface will look crisp, beautiful, and the right size no matter the density of your monitor. Photoshop will now automatically adjust itself based on your Windows settings, making it simple to set up.
Well, thank you for your answer, I've actually figured out somehting like this yesterday but it's still not the most satisfying option but it works somehow. I hope Adobe will change it or at least apply a button or something for changing this in the preset.
The UI scale preference should just be removed it serves not function. Photoshop automaticly use your display the way you have setup windows to handle your displays. There is no Photoshop scaling option now.