auto-create-category.php

if ( ! function_exists( 'auto_create_category' ) ) {

    /**
     * 
     * Create category with specific CPT is create or updated
     * 
     * @author  Everaldo Matias
     * @link    https://everaldo.dev
     * 
     * @version 1.0
     * @license http://www.opensource.org/licenses/mit-license.html MIT License
     * 
     * @see     https://developer.wordpress.org/reference/hooks/save_post/
     * @see     https://developer.wordpress.org/reference/functions/wp_insert_term/
     * 
     * @use     replace 'example' with your cpt name
     * 
     */

    function auto_create_category( $post_ID, $post, $update ) {

        // Only set for post_type = example!
        if ( 'example' !== $post->post_type ) {
            return;
        }

        $title = get_the_title( $post_ID );
        wp_insert_term( $title, 'category', ['slug' => $title] );

    }

    add_action( 'save_post', 'auto_create_category', 10, 3 );

}