Discourse websites may seem slow when updates are occurring, would having a banner any time this occurs be a good idea to inform the users?
Yes, this would be nice if it automatically added this as a banner when updating the forums, especially if people who do their updates monthly or so forth.
But you can, if you do a monthly update or longer, do your own banner notice here from yourwebsite/settings/other and then use the global notice.
If updates are slow when updating then it’s because of limited resource, they do a good job already to avoid that