(I actually have a capture card, but capture cards are essentially virtual monitors.)
I'm trying to mirror my mac on a "display" so I can record it for further reference. I noticed in settings (display) that when you link up the monitor, you have an option to either mirror your main screen (essentially your macbook's POV), or use it as an external monitor.
By default, macOS thinks you want to use the display as an external monitor so you'd have to change it. When I do change it, it remembers my decision for that one monitor.
When I boot into recovery mode, the monitor is treated as a secondary monitor. How do I make it so my macbook treats the external monitor as the primary monitor (or at least mirrors it), so that recovery mode window appears on the external monitor instead of the laptop screen; or other interfaces appear on the external monitor. An example being the first time macOS setup screen/user setup which I have tested on OBS to capture the display and only shows the blurry macos monterey screen. I can also move my mouse cursor to the right onto the external screen.
Significance? - Your laptop screen is broken.