11spd Shimano Road/MTB compatibility
You don't have to mix MTB and road components for this bike. 135mm wide disc hubs with a road 11 speed freehub body exist. I have one on my bike and it's fairly standard for disk brake road bikes with a QR in the rear. 

To answer your actual question:

The compatibility issue between MTB hubs and road 11 speed cassettes is that 100 speed MTB hubs retained the  '10 speed' 34.95mm freehub body, but road hubs went to a longer 36.75mm one.

MTB cassettes generally have larger inner sprockets that can overhang the inboard end of the freehub body and clear the spokes, so a longer freehub body was not needed. Some larger range road cassettes come with a 1.8mm spacer and can fit on the shorter freehub.

If you want to use a MTB cassette with a road derailleur, this can work but you need to make sure you will not exceed the max sprocket size and total capacity of the derailleur.

Specs for Shimano rear derailleurs are here, max sprocket size for RD-R7000 GS (longer cage) is 34 teeth (although many people report you can push the Shimano specs a little, so a 36 tooth will likely work OK).