Screen has support.apple.com/Mac/startup

First, I would recommend doing a restart. You can do this by holding down on the power button until you see the apple logo. If that does not work, try entering recovery mode. There are instructions for an intel based mac: Use macOS Recovery on an Intel-based Mac – Apple Support (AU) and for an apple silicone Mac you can just hold down on the power button until you see ‘loading startup options’. If you find any further details please let me know.