Here are the steps to reproduce the issue:

1. Edit a quiz question in full screen mode on a wide screen. The display is correct with a single scroll bar as expected.
2. Click on the browser "resize" button to narrow the window, or edit the question in full screen mode on a narrow screen (for example a screen rotated 90 deg). In both case, a second scroll bar is then displayed, simultaneously with the other one and which scrolls the same area.

If the second scroll bar is not displayed on wide windows, I think it should not be displayed on narrow windows either. It also makes scrolling a bit awkward on narrow windows.

Please understand that I am reporting this anomaly just in case you haven't noticed it, definitely not as a criticism, but to help you improve the Moodle interface.

I take the opportunity to congratulate the Moodle team for the excellent work they have done, in particular recently for the development of version 4 of Moodle and its great new interface.