There may be times when you don't need the reviewer to give you any feedback, you just want to show them your work, like a brand guidelines document for example. Send them a read-only link that shows them a clean version of your board, with no distracting UI.
Go to the 'Share' icon at the top right of the board
Click on 'Private Link' on the left
Copy and paste the link into an email or Slack etc.