You're right, there is something called a "scrollbar", but many people don't see it because they are using macOS which for some reason hides the scrollbars by default.
Also phones/touchpads don't see scrollbars I think.
Also phones/touchpads don't see scrollbars I think.
My desktop Mac never hides the scrollbar, as it uses a normal mouse, however when I was using a Magic Trackpad the scrollbar would indeed hide unless I was actively scrolling.
Odd behavior.
System Preferences > General > Show scroll bars
• Automatically based on mouse or trackpad
• When scrolling
• Always (because I remember when smart phones didn't exist)
I keep mine at option 3 because I'm a dinosaur