The Mac's hidden scroll bar is normally quite usable in Safari and Firefox, when you move the cursor to the side and start scrolling, it'll automatically pop up, with a thick bar that you can hold on to with the pointing device. That is, unless you are trying to figure out the exact behavior on Chrome or some Electron app, which is half the most used desktop apps on the macOS these days, and took you a while to figure it's actually a bug in Chrome.

https://bugs.chromium.org/p/chromium/issues/detail?id=678537