A PC will never ever use hardware fully, there are too many configurations and variations out there to do so. so yeah you have to spend a ton to get very very high end output.
A console is a set bit of kit that you target it fully and hit the metal to get out as much as you can, its why console games get better over the years as dev's learn the hardware.
So yeah, If a game is made targeting 8k 120fps on a top end bit of hardware then its perfectly doable ( obviously assuming outputs can handle it, HDMI hardware etc ), you just have to design a game and art assets correctly and make the code target that hardware properly to make it do it. its will likely be exclusive to 1 console though as the work to get it running full whack on 2 bits of kit is very heavy.
Bit of background, I've been a pro games dev for 20+ years, I do actually know what im talking about.