Same here, except not with that message. It gets stuck at "10 minutes remaining" and never moves on. I read something about trying it in safe mode, so I'll try that and see if it works.
I get around with it by download the Big Sur 11.4 via the Apple Apps Store. As I too having the same problems downloading via the Software Updates. Have you try to download the Big Sur 11.4 via the Apple Apps Store???? Try that. And install directly to your mac. I had mine already updated!
Have you try type in command line via the terminal with this command.
softwareupdate --fetch-full-installer
Try this one with the terminal
softwareupdate --fetch-full-installer --full-installer-version 11.4
Downloading via apps store fixed it.
I have 230 Mbs stable connection. Over 400 GBs available SSD.
Only issue I recall is not connecting my M1 Macbook Air to a power source during the first attempt to update Mac OS 11.4 via system preferences. I was too lazy to walk to a power source and instead cancelled the update. The issue began with the second attempt to update via system preferences Mac OS 11.4. All fixed by downloading Big Sur in the apps store. I'm guessing this path downloads Mac OS X updater files in a different location or the OS updater metadata needs to record a different update download record.
Same issue here. I am trying for several weeks now. Switched of the firewall. Tried the suggestion of downloading via App Store. But no success so far. What does the terminal do after the suggested commands? Any other suggestions?
I had this problem repeatedly despite good download speed and plenty of disk space. I finally solved it by following the suggestion of going to the App Store and installing Mac OS Big Sur from there rather than running the update in System Preferences.