If you have a Mac, then you should download the latest 'Device Support Update' update which Apple has just released for Big Sur users.
Download the Latest 'Device Support Update' for macOS Big Sur Today to Fix Restore or Update Issues with iPhone and iPad
macOS Monterey is several weeks away and right now those running macOS Big Sur should download the update which has been made available to them over the air. Dubbed as 'Device Support Update,' it basically fixes issues, if you were having any, while trying to restore or update an iPhone and iPad using your Mac.
In order to download this update, simply go to System Preferences > Software Update on your Mac. The update should just show up and you can download it instantly. It spans around 195MB in size and doesn't even require a restart therefore it won't affect your work at hand.
If you are looking to download and install iOS 15 and iPadOS 15, then be sure to check out the following:
iOS 15, iPadOS 15 Final Download for iPhone and iPad is Now Available









