In some apps and browsers, there’s an option to enable overlay scrollbar (or is enabled by default). By saying overlay scrollbar, I mean a transparent scrollbar which hides when the mouse no longer covers it. It doesn’t move or change website content in any way like default one does in Firefox or Thunderbird.
GIF 1 contains default scrollbar in Firefox 111.0.1 (64-bit) (no option to enable the overlay scrollbar).
GIF 2 contains overlay scrollbar in Chrome 111.0.5563.11 (Official Build) (64-bit) after enabling the “Overlay Scrollbars” flag in chrome://flags.
GIF 3 contains overlay scrollbar in Spotify for Windows 126.96.36.1997.g2b3ce637 (scrollbar is enabled by default and not changeable).