macOS High Sierra and macOS Mojave upgrade solid-state drives to Apple File System (APFS), which requires Startup Manager to switch between Windows and macOS.
If you choose "Restart in OS X" from the Windows Boot Camp menu, this message might appear: "Could not locate the OS X boot volume."
Follow these steps to boot into macOS or Windows:
- Restart your Mac, then immediately hold down the Option key.
- Release the Option key when you see the Startup Manager window.
- Select your macOS or Windows startup disk, then click the arrow or press Return.
Repeat these steps any time you need to switch between operating systems.
If you use a screen reader
If you use VoiceOver or another screen reader and you need further help switching between Windows and macOS, please contact Apple Support.