I’m not entirely clear on what you’re trying to accomplish in terms of the page height. The visible part of the page is going to vary tremendously depending on what size screen the site is being viewed on, how big the browser window is, whether the browser is stock or has the top menu enabled (Firefox) or bookmarked icons, or extensions that add rows to the top or bottom reducing the viewable area of a website page. Some people hit F-11 when they browse to use the entire monitor to see the site. Some people enlarge the website to make the text bigger using the magnification options (like I view Facebook at 110% enlarged to help my poor old eyes.) All these things can throw off your “best laid plans” of how you want users to see your website.
1920px by 1080px is the full display area of a typical widescreen monitor, but that doesn’t mean that’s what people looking at your website are going to see in their browser. If fact, many (if not most people) have their browser window reduced in size, in which case all your efforts to make specific sections of the page appear at specific points… well… pointless.
What’s probably more important is to shoot for clear visual delineation between sections either using different colored background, or graphic page dividers. Lately I’ve been doing stuff like this to separate sections of my pages…
but I can’t possibly guarantee that a person is seeing any particular area in a single “chunk.” That’s why I use the colors and curved graphics to separate one section from another. I think this is most important on mobile screens since a single background color on a very tall page becomes an exercise in scrolling monotony for the user. Alternating background colors seem to be the popular go-to for separating areas of “tall” pages.
Regarding the Galaxy fold, using Chrome’s F-12 inspector and the Galaxy fold emulation, your site seem to look fine except for that first section where you “create an account.”
I downloaded your test file and I’ll take a closer look at it tomorrow.
One other thing I noted… the location of your fixed “scroll to top” button (the arrow in the circle) is very distracting and obstructing on mobile. It needs to be lower, more to the right, and smaller, maybe even partly see-through (like 50% opacity) Like 40px x 40px and about 10px from the right and bottom.