If you want to install macOS on an Intel-based Mac but receive an error related to external startup disks, what should you do?

When installing macOS on an Intel-based Mac and encountering an error related to external startup disks, temporarily changing the External Boot setting is the appropriate action to take. This setting determines whether the Mac allows booting from external drives. By adjusting this setting, you can enable or disable the ability to boot from an external disk, which can resolve the installation error you are experiencing.

Sometimes, security settings or existing configurations may prevent the Mac from recognizing the external drive as a valid startup disk. Making this temporary change can help facilitate the installation process by ensuring that the system is prepared to boot from the external drive that contains the macOS installer.

Updating macOS, disconnecting the Ethernet connection, or using a different external drive may not directly address the core issue of booting from the external disk, as the problem lies within the boot settings specific to the device's firmware or security configurations. Therefore, adjusting the External Boot setting can provide an immediate solution to proceed with the installation.