Hello and welcome to the forum :)
The way the feature is designed, the notification will not re-appear for a user, when they click on the X - unless yet another new version has been released, which resets the notification.
You can stop new notifications, if you disable the update check in the scheduler (s. Admin panel -> Scheduler -> Check for platform updates). Once disabled, each admin user that still sees it, has to click on the X one final time to remove the notification from then on.
Compliance can be a reason to postpone updates - security is usually the opposite. Generally, when aiming for security, you want updates as soon as it´s sensible to roll them out.
