Unlock the disk that I want to install macOS

Follow the good advise from previous posting.

From the Link in that posting >>

Follow these guidelines during installation:

• If the installer asks to unlock your disk, enter the password you use to log in to your Mac.
• If the installer doesn't see your disk, or it says that it can't install on your computer or volume, you might need to erase your disk first.
• If the installer offers you the choice between installing on Macintosh HD or Macintosh HD - Data, choose Macintosh HD.

The OS X Base System disk cannot be installed onto. It's a read-only volume.

It appears you don't have a properly formatted and recognizable drive volume on which to install macOS.

Please see this support article:

How to reinstall macOS - Apple Support