I'm very familiar with websites switching to mobile layout with hamburger menu instead of a navigation bar, when you reduce the width of the browser window on your desktop. BUT I don't think I've ever come across a resolution change where the website elements (either hamburger menu or content) get massively larger.
Can you provide an example of one or two mainstream sites that change resolution like that?
The reason I'm confused is because in CSS everything is based on logical pixels, not actual device pixels. E.g. a "1 px" width will be 2 or 3 hardware pixels wide on an iPhone. Similarly "1 em" will be 16 hardware pixels on a standard resolution display, but 32 or 48 hardware pixels on a 2x or 3x display. So web designers don't have to do anything special to accomodate hi-DPI screens in the first place.