Howdy!
Sorry for the confusion here. Diablo IV does not offer a fullscreen mode, the resolution box being grayed out is under investigation. Note the game only supports 9:21 not 9:32 so you will see black bars on both sides of the Samsung G9 unless you play in Windowed
mode at certain screen sizes. Resolution Percentage can’t be changed if you have FidelityFX Super Resolution 2 options selected. If you set, “FidelityFX Super Resolution 2” to None, then Resolution Percentage should allow to make adjustments. If it’s not doing with the selections made, make sure to bug report that over on our Bug Report forums.
Thank you.