If you’re trying to download macOS Big Sur right now, good luck. It appears the huge demand for the 12.18GB macOS upgrade has caused Apple’s servers to melt.
When you click ‘Upgrade Now’ on your Mac, users are being greeted with the following error message: “Installation failed. An error occurred when installing the selected updates.”
Repeated attempts to download the upgrade result in the same error. Even if the error message disappears, the download just hangs with the “Downloading new updates” message.
Also, Apple’s developer is down right now too, which may be a result of the huge demand for macOS Big Sur.
Again, if you’re not in a rush, try downloading Big Sur later tonight or on the weekend. It may not be worth the aggravation and lengthy delays.