News EK Announces Vertical GPU Mount For RTX 3080, RTX 3090

Or you can put some kind of support between the bottom of the chassis and the corner of the card that is "in the air" so a heavy card will not sag or bend the motherboard and it will also not block your slots.
 
One of the benefits of watercooling besides lower temps , is freeing up space for other cards and freeing space for air flow between cards so they are not close to each others from huge GPU cards ..

water-cooling vertical mounted GPU and losing all the slots behind is a waste of space ...