Tall an' handsome

An OS related update for the MAC version of M2TW makes it impossible to play the game without updating the OS to 10.14

There is now a workaround for those that do no wish to upgrade their OS:

Originally Posted by Feral on Steam

Players using a version of OS X before 10.14 can access a compatible version of the game via the Beta tab in the game’s properties window. Select the ‘mac_linux_gl-1.0.3' branch for a version that is compatible with 10.10.5 up to 10.13.6.

1. Launch Steam.
2. Right

...