On iOS you can trick the page into scrolling horizontally by selecting some text and dragging the selection marker beyond the right edge of the screen. Still an annoying workaround though, because the page snaps back to the left as soon as you try to scroll vertically again.

Ah, yeah, I see now. I can recreate the problem on desktop. On my mobile it works. Indeed, the scrollbar is implemented to override the browser's.

Why go to archive.ph, though, when you can go directly to https://melsloop.com/docs/mels-hack-the-missing-bits ? - should work nicely on mobile.