Completely turn off internal display and use external display on an iMac 24 2021 M1

[jayyoungdesign]

The internal display of my iMac 24 M1 2021 is failing quickly and I need to turn it off completely and use an external display as my main display. I bought BetterDisplay reading that it can do this. I am so far unable to figure this out. I need step by step guidelines. I am running the current Tahoe OS.

Thank you for any and all assistance!
Jay

[waydabber]

Hi there,

sure, you should configure the external display as main display and simple use the display header to turn off the built-in display.

But: for an iMac you'll need to disable this failsafe first:

[jayyoungdesign]

Thank you for your reply.
I need specifics on how to configure the external display as the main display.
I do not see how to use the 'display header' to turn off the built-in display.
The external display is an HPZR2440w and it is plugged into a powered USBc in the back of the iMac.
Best, Jay

[jayyoungdesign]

I currently cannot get either internal or external screens to show, meaning I am not able to login and get running. I have tried holding the power button to get startup options but still nothing. Please help!

[waydabber]

Well, without a built-in display (as I understand it is broken) to log in and boot, and no configured Screen Sharing, it will be extremely difficult to log in to your iMac and configure the app I am afraid. The external display not producing an image during pre-boot may be normal.

You'd need to log in somehow, configure the app, enable built-in disconnect for iMac, then disconnect the built-in display so the sole remaining display is the external display - then make this a kind of default with a login script that does this for you. You can't fully disable the built-in display for an iMac in a way that it survives reboot.