To successfully set the background color when using image as a launch screen:
create a Color Set in Assets.xcassets, name it, eg. splash-background-color
add in Info.plist "Launch Screen" > "Background color" > enter named color eg. splash-background-color
restart iOS Simulator - this is crucial (and stupid) ! Xcode 26.0 will show you just a blank screen until you restart simulator after any Launch Screen related changes! Clean does not help