Razor has a 17” laptop that can be configured to have a 4K display, but you also have to upgrade the GPU to a RTX 2080 Max-Q. The RAM and storage is end user replaceable though and you’d have an absolute beast of a machine that could handle pretty much anything you’ll ever throw at it. It is $3700 though.
https://www.razer.com/gaming-laptops/razer-blade-pro/shop
There are some 4k models, but those bring more weird fractional scaling problems with them (especially bad on Linux), have battery life and are usually super expensive.
Oh ... and it's all 14 or 15" models. I'd happily take a 17 or 19" laptop - I just want enough portability so I can carry it around in a bag while commuting and have it on a desk most of the time, but, while there are some okay 17" offerings (barely any "pro" devices, though, so no swappable RAM) there is not one (apart from the insanely expensive ZBook) offering with a higher than FHD screen.
What the fuck?! Why? Don't most people use their laptops as only somewhat portable work stations? Am I the only one who finds a larger screen with more content useful?
?!?!?!!?!?