> Upgrade from macOS Sierra to Big Sur
My 2017 iMac Retina 5K 27–inch has an internal SSD and is ready to be upgraded from Sierra to Big Sur. What’s the best way?
That’s a giant leap for a Mac, which requires converting your startup disk to APFS and total reorganization for Big Sur’s new Sealed System Volume. Many of your apps may also require major updates. It may be wise to perform a clean install, then migrating from a clone or backup.
To do that properly, you should install Big Sur on an external disk and copy the installer app there. Restart from that, format your internal storage, and install macOS 11.0.1 onto that. Do that with your clone or backup connected so that when the installer prompts you to migrate from another system you can select that disk as the source.
Although a direct install using the downloaded Install macOS Big Sur app should still work, it has a lot to do and the risks of it stalling somewhere are significant. Once it has completed, you’ll still have plenty of cleaning up to do. If you have problems with the installer app not completing, try making a USB bootable installer using Apple’s instructions at bit.ly/mac361osinstall. Flash memory “sticks” can be slow, and a small SSD works better. Ensure you format it first in HFS+ not APFS.