Galaxt S9/S9+: What to do when screen is cropped and colors are different on monitor?
If you only see a part of the screen or different colors on your TV or monitor, go to the Settings menu of the relevant display, and try to resolve the issue to some degree via the Color/Resolution settings or Screen Size settings.
Currently, Samsung DeX itself doesn‘t support a feature for changing the resolution.
The access to and name of the settings menu may vary depending on the TV or monitor.
Samsung DeX officially supports Full HD (16:9, HDMI supported) monitors. If your monitor only supports a resolution below Full HD or is defective, the Samsung DeX screen may appear blurry.
Also, Samsung DeX mode supports HD+ and WQHD resolutions, where some content on your device may be displayed differently on the TV or monitor.