I see you already reviewed similar issue at i7 8700k Intel Graphics Installation Error
Do you actually see the iGPU in device manager?
To bypass message "best driver is already installed", "customized computer manufacturer driver" or "computer is not validated" install driver via have disk method as described at:
https://www.windowscentral.com/how-install-intel-beta-graphics-drivers-surface (ignore prolog about MS surface)
Problem solved. After 2 day actualizaciones last actualization W10 it solved. Driver for VGA successfully install. Thx.