Buy the game Monochroma some time ago and no one achievement has earned until I passed it. Already trying to get help in steam forum, but nothing. Maybe anyone have this kind of problem on mac platform with steam games? Thanks for watching!
Steam uses OS X's Accessibility API for the Steam Overlay (Shift+Tab screen) and to communicate between the game and Steam.app. You probably enabled it when you installed Steam. Unfortunately, every time you update Steam (this is a bug in OS X) you must uncheck and re-check the box in System Preferences. If you're having this issue on your Mac but not Windows, that's the reason.
Just go to System Preferences > Security & Privacy > Privacy > Accessibility, unlock using the icon in the bottom left, and uncheck and re-check Steam.