I have Chrome, version 76 as of writing this, on Windows 10, all updates installed.
I have 2x 4K displays, one Asus MG28U and one Samsung U28E590. I have set my Nvidia 1060 graphics card to display in 4K, 200% font sizing.
All this works wonders. I have crystal clear 4K text and graphics in all applications, including Google Chrome and websites.
Except for one thing, when I look at Youtube videos that has both 4K in the title and also this 4K small label, the quality choices go up to 1080 and no higher.
Is there a trick to enabling this? I tried to see if changing font scaling to 100% enabled it but that does not alter this outcome.