Gukesh repeatedly played opening lines that went out of book shockingly early. No amount of prep can prepare you adequately for someone willing to go off script on move 6.
That is what high level chess has been for years: preparing lines where you have the disadvantage if your opponent plays perfectly, but it uses up their clock and gives you opportunities to punish mistakes in their calculation.
The same technique is used in ameture level chess too, although these are more likely to be piece gambits than merely positional ones.
