Restrict login of the admin user using the login of the ultimate member

@ziemowit1

You can try this code snippet

add_action( 'um_submit_form_errors_hook_login', 'custom_submit_form_errors_hook_login', 10, 1 );

function custom_submit_form_errors_hook_login( $args ) {

    if ( isset( $args['username'] ) && ! empty( $args['username'] )) {
        $login_type = 'login';
        if ( is_email( $args['username'] )) {
            $login_type = 'email';
        }
        $user = get_user_by( $login_type, $args['username'] );

        if ( in_array( 'administrator', $user->roles )) {
            UM()->logout();
            exit( wp_redirect( home_url() ) );
        }    
    }
}

Install by adding the code snippet to your active theme’s functions.php file
or use the “Code Snippets” Plugin

https://www.ads-software.com/plugins/code-snippets/

Nothing more to add, it just works.

Thank You @missveronicatv.