Download fail message when downloading macOS Big Sur 11.2.3

Hey there!

Safe boot was my first thought as well.

Are you downloading it from System Preferences > Software Update?

Or from the App Store?

If from System Preferences, I’ve heard deleting that installer from the Applications folder, searching the App Store for “Big Sur” and running that may do the trick.

Otherwise, I know Big Sur requires much more temporary storage to install, can you say how much free storage you have on your Mac?

Apple > About This Mac > Storage.

If you’re already on an earlier version of Big Sur, it may not matter as much, but still may.

Otherwise, I may try disconnecting my router from power for a minute, reconnecting it.

Then, create a new network location:

https://support.apple.com/guide/mac-help/use-network-locations-on-mac-mchlp1175/mac

Then try running the update again.

If no luck, sometimes running the update from another admin/user may do the trick, if there’s any conflicts in your user profile.

If all else fails, you can try another network, (Even though yours work fine on other devices), OR:

If using an Intel Mac, Boot your Mac to Internet Recovery and Reinstall the latest available version:

Startup your Mac while holding Command Option R, let go when you see the globe icon.

Once there, choose the option to Reinstall Mac OS, this would install the latest version.

If your drive doesn’t show up as an option to install to, it maybe locked via FileVault or Find My:

In that case, go to Disk Utility, click on the greyed our Macintosh HD, click File > Mount and enter an admin password. Once done you can quit the again try to Reinstall the OS.

I’d try the other steps first as there’s usually no need to reinstall an entire OS for an update, but sometimes maybe the case. Always a good idea to keep one, two or even more backups! Good luck! Hope you find an easy way to do it!