How do I get reusable blocks via frontend REST API?

How do I get reusable blocks via frontend REST API?

We need to be logged in as a user and additionally add the wp_rest nonce to the block rest endpoint request, either via the _wpnonce POST/GET parameter or via the X-WP-Nonce header.

See e.g. the docs for more information on the authentication.

EDIT: As pointed out in comment, to do what questioner is trying to achieve you would need to create a custom endpoint without authentication as the existing block endpoint checks permission of current user.