Created attachment 8568
The problem is basically outlined on a screenshot.
Reproduce in the following way:
1)Connect a second monitor (e.g. on a laptop).
2)Observe that there is no Alt-hotkey assigned to 'Advanced' to go an original settings screen.
I think this is a bug.
Simon Steinbeiss referenced this bugreport in commit 7985880ffe136f7e0542140c60fee9b70bc7ed6b
display: Add mnemonics to minimal dialog buttons (Bug #15449)
Unfortunately we cannot easily add mnemonics to the other monitor layout options, as those are radio buttons and not regular buttons.
I however added it to the "Advanced" button.