The erase button is grayed out in disk utility

Hi,

Are you booted into Recovery? Have you selected the top item in the list on the left? See Step 7: What to do before you sell, give away, or trade in your Mac - Apple Support

Are you sure your Mac is shut down? Hold down the power button for about 10 seconds if you need to. Then hold down and keep holding down the Command and R keys and press the power button. Don't release Command and R until it's booted into Recovery.

You're welcome.