Full Screen Desktop Resolution
Full screen uses a borderless window at your native desktop resolution to allow for quick alt-tabbing to desktop and other applications without disruption.
If you're playing on an older or lower spec GPU then try SETTINGS > GRAPHICS > RESOLUTION SCALING > SUBSAMPLE (75%).
Subsampling does not pixelate the user interface.
If you have a high spec GPU then you can also supersampling.
You can increase or decrease the GUI size using SETTINGS > GAMEPLAY > GUI SIZE.
Save will make changes permanent. Cancel will temporarily change.