🙄 Of course, I found the solution shortly after the post.
function example_block_category( $categories, $post ) {
return array_merge(
$categories,
array(
array(
'slug' => 'example',
'title' => 'Example',
),
)
);
}
add_filter( 'block_categories', 'example_block_category', 10, 2);
