Using APM Planner v2.0.14 on a MAC I entered full screen mode and got trapped. There is no listed key to get back to Normal mode.
Many media players use the “Esc” key for this function and I suggest adding it to the command set.
Right now the only way out is to use the F3 key to bail out or to mouse up to the top of the screen and get to the “View” pulldown menu. Neither of these methods is particularly intuitive or fast.