How to keep the capability of users and disable Gutenberg editor in WordPress?

add these lines in your ‘functions.php’, it will work

//if not gutenberg reapprove posts
add_filter( 'wp_insert_post_data', 're_aprove', '99', 2 );
function re_aprove( $data, $postarr ) {
    //check if current user is not admin
    if ( ! current_user_can( 'manage_options' ) ) {
        if ( 'publish' === $data['post_status'] ) {
            $data['post_status'] = 'pending';
        }
    }
    return $data;
}