The Vram availability that is displayed on the fps window is the actual amount available to the sim. The fact that it shows only 10.8GB out of 12GB is because of normal overhead that is outside of the sim along with any Vram being used by another process/app. Just like a file subsystem like NTFS never shows the actual total amount of real disk space because there is a little overhead to account for along with apps like the Recycle Bin.
That video looks to be about 8 months old so was recorded prior to a recent sim release (SU15 I think) which changed how much Vram was being displayed in the fps window. Prior to the release, the Vram in the fps window was displayed as total Vram of the video card. With SU15, the Vram displayed is now the total Vram available to the sim after accounting for the overhead & other processes/apps. MS/Asobo indicated the change was done to more accurately show how much Vram the sim actually had available for it to use.
So the bottom line is that all is good with the Vram availability on your 4070 super and no Vram is “missing” 
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