Broken: 2.80 (sub 64)
Worked: 2.80 (sub 60)
Short description of error
It's already been mentioned in T64888 - Fullscreen Area Button conflicts with Sidebar.
There is a button to exit the fullscreen area (Toggle Fullscreen Area) in the upper right corner.
After some changes it became invisible.
Worked: version: 2.80 (sub 60), branch: blender2.7, commit date: 2019-05-07 19:17, hash: rB3dc9da3a74ee
Broken: version: 2.80 (sub 64), branch: blender2.7, commit date: 2019-05-13 22:40, hash: rBf070bdd7c9c4
Since there is no menu in the fullscreen area,
and the default Ctrl/Cmd-Alt-Space shortcut is not available on Mac,
this button is the only way to exit fullscreen.