No, it clearly is showing that the Vram will cap at 3GB instead of potentially using all 4 GB. It seems obvious to me.
I have been having problems with Rx580 vram usage with Prepar3Dv5 (directx 12 simulator). Everytime the sim says I am out of Vram when I still have 1GB or a bit more free Vram in GPU-Z.
It seems to me that Vram usage in Windows 10 is not optimized for the Rx580. Amd just forgot about this card that still has so many problems.