Me neither. I play at 1440p/120hz. Both cables can manage that resolution and frame rate.

The only difference I get is when I use DisplayPort and leave my computer alone for 20 mins, the GPU goes to sleep and the monitor won’t display anything although I hear background apps/games running.

Without changing any settings, using a HDMI cable solved that.

HDMI it is.

First, you want to play on high/60fps but at what resolution? Paying over 1700$CAD for a RTX4090 GPU seems overkill while a RX6800 or a RX7700/7800 would let you play at 1080p/1440p at high settings at a fraction of the price.

SSD is fine.

PSU could be reduced to 850W.

64GB RAM is overkill for gaming right now but potentially useful in the upcoming years.

Bottom line, you could save here and there and still have a capable AM5 machine.

If you want value for your buck, build yourself an AM4 machine. Yes, AM5 is out now but your rig could still last you many many years with the right AM4 components.