Can the built-in display turn off automatically when I use an external monitor?

Yes. On a supported Apple silicon Mac, enable Disconnect built-in display when an external display is connected under Settings > Displays > Overview > Display Connections > Connection Management Settings…. This Pro feature disconnects the built-in screen when a suitable external display is connected, including when the external display reconnects after wake.

The rule depends on an eligible external display becoming available. It is not simply a timer that turns the built-in screen off after every wake. BetterDisplay virtual screens and displays classified as system virtual, such as AirPlay and Sidecar, do not trigger it. If the external monitor takes longer to reconnect, the built-in screen can remain available during that interval.

For a rule that applies only to particular monitors, enable Ignore for built-in display auto-disconnect under the other monitors’ Settings > Displays > [display] > General Settings > Additional Settings…. Leave that exception off for monitors that should trigger the rule.

Keep Allow disconnecting all connected displays off unless you specifically need it and have planned recovery. Enabling it disables automatic reconnection when no eligible display remains. You do not need to enable it merely to use the external-display rule. Some built-in displays also have model-specific safety restrictions. Read Display Connections before changing those overrides.

Manually reconnecting the built-in display can temporarily suspend the automatic rule. If your goal is instead to reconnect it through automation and leave it on, see why it turns off again after a Shortcut reconnects it.

For a manual test, desk automation, recovery checks and a complete undo procedure, follow Use external monitors with your MacBook open and its built-in screen disconnected.