Starting today, customers are able to view the latest macOS versions supported on their EC2 Mac Dedicated Host, which enables them to proactively validate if their Dedicated Host can support instances with their preferred macOS versions. As each macOS version requires a minimum firmware version on the underlying Apple Mac to successfully boot, a host may not support booting the latest macOS versions if the firmware on the Apple Mac is outdated, which may happen if an allocated Mac Dedicated Host has remained idle for an extended period of time. To ensure supportability for the latest macOS versions, customers can launch and terminate instances on their allocated Mac Dedicated Host which will trigger the host sanitization workflow and update the firmware on the underlying Apple Mac. A Dedicated Host with a long running instance will be updated automatically when customers stop or terminate their running instance.
Source:: Amazon AWS