Set Display Name to Username on Registration

<?php
if ( ! function_exists( 'scseed_set_display_name_on_register' ) ) {
    function scseed_set_display_name_on_register( $user_id ) {
        $user = get_userdata( $user_id );
        if ( ! $user || empty( $user->user_login ) ) {
            return;
        }
        wp_update_user( [
            'ID'           => $user_id,
            'display_name' => $user->user_login,
            'nickname'     => $user->user_login,
        ] );
    }
    // Priority 20 runs after WordPress's own user_register hooks.
    add_action( 'user_register', 'scseed_set_display_name_on_register', 20 );
}