Installed Big Sur and now Safari doesn't work

Startup in Safe Mode:    https://support.apple.com/en-us/HT201262

    Login to your account.

    Launch Safari and test.

    To exit Safe Mode, click  in the menu bar and choose “Restart”.

    Test.

    Launch Safari holding  the shift key down and test.

Why do you mean "now Safari doesn't work"? Please be more specific and provide us with more precise details of what happens. What messages you are receiving, etc.

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