1440p 120Hz gaming is sublime. The pixel density of 1440p is perfect for a 27" screen. Running 4K resolution on that same screen makes exactly zero visual difference, but costs significantly more processing power.
1440p 120Hz is the porridge that's just right for PC and console gaming. Next-gen 4K 120Hz or 8K gaming is a myth concocted for the sole purpose of selling HDMI 2.1 screens. Existing HDMI 2.0 screens, HDMI switches, HDMI splitters, HDMI cables etc can run 1440p 120Hz.
There is no reason at all to go beyond 1440p for desktop gaming at 16:9 screen dimensions. Ultra-wide 21:9 gaming is still best constrained to 1440p pixel height, but with added width.
If you're gaming from the couch however, 4K will be a noticeable visual upgrade on 40" or larger screens. But it comes at the cost of lower framerates, which is the real performance handbrake. Once you've tried buttery-smooth 120FPS, it's near impossible to go back to stuttery 60FPS.
None of us will be getting 4K 120FPS out of next-gen consoles...it's only possible on an RTX 3090 GPU, which alone costs thousands of dollars more than a Series X or PS5. The performance we get out of a Series X running 1440p 120FPS is phenomenal bang-for-buck.