Mission Planner Mac only displays in partial window

#### Issue details
When Mission Planner is opened on the Mac, the Mission Planner display doesn't take up the full Mac window and is displayed with grey borders on the right and bottom.

This was working as recently as December 2021.

#### Version
Latest daily as at 6 Jan 2022

#### Platform
[ X] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
_What type of airframe (flying wing, glider, hex, Y6, octa etc)_

#### Hardware type
MacBook Air 2017 running 11.6 Big Sur

#### Logs
Screenshot attached

Reproduce the partial-window display on a MacBook Air running Big Sur using the latest daily build, and compare it with the behavior reported from December 2021. The issue names no source file, entry point, or test; done means the Mission Planner window fills the Mac window without the grey right and bottom borders.

Written by the indexing model from the issue text.