When scrolling/reading a web page, it literally changes that section of the text so that it fades to gray.
So, "everything scroll fades".
I couldn't find a way to turn it off. Quite irritating, IMHO.
EDITED TO ADD ELABORATION: The issue with iOS "scroll fade" text color in Safari near the top notch is that this makes that top-edge-text "dynamic" (changing) and thus "draws attention" to it visually, thus competing for eyeball attention when I am probably actually reading somewhere further down on the page. Also, I would still like to be able to glance up to the topmost visible text if wanted, without having to adjust to its different and less visible colors. Apple designers should know all this. Further, I'd say the page text color should probably by default respect what the web page designer configured it as, and not have the OS change that text color (unless the user gets fancy and requests an override with dark mode or whatever settings).
This article's critique seems valid, too (more generically about "scroll fade" in interfaces, e.g. web pages, which seems to mostly be about items appearing gradually via motion). Personally, I see less of that these days, compared to making every page in an OS fade out where unnecessary.