Make specific post IDs in a restricted category available publicly.

unlock_posts_by_ID.php

<?php // Do not copy this tag
/*
 * Make specific post IDs in a restricted category available publicly.
 *
 * Add this code below to your PMPro Customizations Plugin - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function unlock_posts_by_ID( $hasaccess, $post, $user, $post_membership_levels ) {
	// If they already have access, let them at it.
	if ( $hasaccess ) {
		return $hasaccess;
	}

	// Set which post IDs are public.
	$public_post_IDs = array( 1, 2 );

	// Now check the post ID
	if ( in_array( $post->ID, $public_post_IDs ) ) {
		$hasaccess = true;
	}

	return $hasaccess;
}
add_filter('pmpro_has_membership_access_filter', 'unlock_posts_by_ID', 15, 4);

This recipe is included in the blog post "How to allow visitor access to specific posts in a Membership-restricted category." at Paid Memberships Pro here: https://www.paidmembershipspro.com/how-to-allow-visitor-access-to-specific-posts-in-a-membership-restricted-category/