That is only shown in debug mode. You shouldn't be running debug mode in production, or if you are, it should be gated behind known admin IP addresses.
The upgrade cannot be completed unless the user logs in as an administrator.
Ultimately, it literally doesn't matter if it's shown in debug, or not, or to guests, or not, because anyone who knows anything about XenForo could access that link anyway, but not be able to use it unless they are logged in.
I don't want users to see that message cos it doesn't concern them.
If the upgrade enables debug mode.
And the message is shown only in debug mode to all users.
My suggestion is valid, don't show it to non staff members cos it's not for them.-
Ok, but what about debug mode being enabled makes the message relevant to non staff?
I don't understand this logic at all: "debug mode is ON therefore this message has to be shown to everyone".