To this day I am embarrassed to discover entire options in apps I had been using for ages, that were hidden behind invisible scroll regions. I even reported a bug once because I thought a feature was removed in an update, when in reality it was just a stupid default clipping issue with no visible scrolling.
When something looks like two simple controls in a small rectangle, and you have to accidentally shuffle your trackpad over it to figure out that it will move to reveal a dozen more controls, that is a failure of design.
When something looks like two simple controls in a small rectangle, and you have to accidentally shuffle your trackpad over it to figure out that it will move to reveal a dozen more controls, that is a failure of design.