The scrollbar is not reliable. On Apple platforms, they hide the scrollbar unless you’re scrolling. I think CSS lets us specify that it should be visible on our own pages, but I don’t know how that interacts through browsers to the native behavior.
Progress meter is also at 0% when you're not scrolling, so unless you scroll, you don't know how much text there is to read.
(btw, just checked for Firefox and Safari, and the scrollbar is visible at all times, unless the website explicitly hides it)
There is a setting for this called "Always show scrollbars" and I know it defaults to off for me. The underlying about:config rule is specific to GTK though, so this may be platform-specific.
But also I don't really get how people are fine with hiding the scrollbar, but prefering to see the progress meter always visible for text, when the scrollbar conveys mostly the same information (except some edge cases when the footer is long I guess).
Not that it's important at all, I'm just at loss and it's not the first time I'm getting a signal that sometimes I simply don't understand people. But of course that's fine.
On macOS, at least, this is a setting so you can make them visible or invisible according to your taste. Probably not available on phones, though.