How to unlock an iPhone?

Are you asking about an iPhone – as the new title that the Moderator gave to this thread implies? I've never heard of an iPhone displaying a screen that looks like that.

Or were you asking about a Mac mini running macOS 10.15 (Catalina) – as your tag line implies? A Mac mini that is running Catalina would be an Intel-based Mac mini, and the screenshot you posted looks an awful lot like a prompt for a firmware password.

Set a firmware password on your Mac - Apple Support

If that is a firmware password prompt, it will appear whenever you try to enter Recovery Mode, or try to start up the Mac from a drive other than the designated startup drive.

You can't turn off a firmware password unless you already know it. If you have forgotten the password, you'll need to bring the Mac and its original receipt or invoice (as proof of purchase) to Apple, or an Apple Authorized Service Provider. If you have neither the password nor the required proof of purchase, the Mac will remain locked.