Broken MacBook Pro screen

Hi,

It could be possible your screen is still alive even if startup in black screen.

If your Mac starts up to a blank screen - Apple Support

If it doesn't help, trying following tips.

On your keyboard, press Command and F1 together and see if it enables mirroring. If it doesn't, then press Command, Fn, and F1 keys together.

Just connect the external display or TV set. When everything on the cable is up and running, connect the end of the cord to the Mac LAST. If you get ANY picture, it is working as designed.

If it only shows desktop background, and not the menubar, you can toggle the sense of "Mirror displays" easily, just as kaz-k has suggested. I say Command-BrightnessDown because I can remember it more easily and it works with Touch Bar, but it's the same command.