how to install big sur
InstallAssistant.pkg for Big Sur 11.7.10 will not open.
MacBook Pro 13″, macOS 11.7
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Start up from macOS Recovery
Command-R is generally recommended, especially if you never installed macOS Sierra 10.12.4 or later… How to reinstall macOS - Apple Support
Command (⌘)-R
Install the latest macOS that was installed on your Mac.
Option-⌘-R
Upgrade to the latest macOS compatible with your Mac.
Shift-Option-⌘-R
Install the macOS that came with your Mac, or the closest version still available.