This issue is a follow-up from MDL-80052 from one of the comments the awesome reviewer/integrator sarjona left as optional:

B. [OPTIONAL] Around line 98 in badges/view.php, I would suggest replacing the legacy box with a notification:

echo $OUTPUT->box(get_string('error:notifycoursedate', 'badges'), 'generalbox notifyproblem');

with

  echo $OUTPUT->notification(

        get_string('error:notifycoursedate', 'badges'),

        \core\output\notification::NOTIFY_WARNING,

        false

    );

If you decide to change it, you'll probably need to update badges/index.php too.