I have purchased a rog certified genome and and am a happy customer that has built my first pc. So the grommets in the rear panel are for diy custom loop support or some sort of cable management?
And the angled bracket that "isolates circuitry" has 8 mounting holes but I'm unsure what it is meant to accommodate?
the holes in the second pic as others have said are for watercooling. they are for an externally mounted radiator or even res. Simply put they are rubber grommets for the pipes to go through.