Disable default block theme patterns

To disable the default block patterns in WordPress (so only your custom patterns are available), use the following method in your custom blank theme:

<?php
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

add_action('init', function() {
    remove_theme_support('core-block-patterns'); // Disable default block patterns
});

add_filter('should_load_remote_block_patterns', '__return_false'); // Prevent fetching patterns from WordPress

Add this to the functions.php or you can use code snippet editors.