Install Windows 11 Without Internet (BypassNRO)

On the screen that asks you to connect to a network, press Shift + F10 and run:

oobe\BypassNRO

The PC restarts and the network screen now shows I don't have internet. You can continue offline with a local account.

If the script is missing (Microsoft removed it in recent builds), set the value by hand and restart:

reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\OOBE /v BypassNRO /t REG_DWORD /d 1 /f
shutdown /r /t 0

Microsoft keeps closing these workarounds in new builds. If none works, use an unattended answer file.

Related: use a local account in Windows 11 setup.

More info.