On iPhone and iPad, when you're scrolling a long document, like a web page in Safari, a scroll bar shows up on the right side of the screen. In early iOS versions this was just a way to tell where you are on the page, but since iOS 13 you can use it to scroll, like on a Mac.
Starting to scroll a page by swiping up or down, then when the scroll bar appears, long-press on the scroll bar and drag it up or down.