How to save preferences interface UI Scaling?

What OS version are you using??

High-density monitor support and per-monitor scaling

New in the January 2018 release

High-density monitor support and per-monitor scaling

On Windows 10 Creators Update and later versions, Photoshop now offers a full range of choices for UI scaling—from 100% through 400% in 25% increments. This enhancement makes the Photoshop user interface looks crisp and sharp regardless of the pixel density of your monitor. Photoshop automatically adjusts its resolution based on your Windows settings.

In addition, Adobe and Microsoft have worked closely to provide per-monitor scaling across monitors with different scaling factors. This enhancement ensures that a high resolution (HiDPI) laptop works seamlessly alongside a lower-resolution desktop monitor, or vice versa. For example, one of your monitors can have a scale factor of 175%, while another monitor can have a scale factor of 400%. So, you can choose either the highest-end 13-inch laptops with 4k screens, the more affordable 1080p models, or tap into the new 8k desktop monitors, and still have an uncompromised experience within Photoshop.

In Windows, select Start > Settings > System > Display. Now, under Scale And Layout, choose a scaling factor for each of your displays.

Note:

On Windows 10 Creators Update and later versions, the UI Scaling setting in Photoshop (Preferences > Interface > UI Scaling) still applies to some components, such as the File Info and Camera Raw dialogs.

On earlier versions of Windows, this preference applies to all Photoshop components. When the UI Scaling option is set to Auto, scaling defaults to the value closest to the primary monitor's OS scaling factor—100or 200.