I did not plan on running the iOS 12 beta so I was running 11.4.1 on my phone and started getting the annoying pop-up message. I went to the Software Update on my phone and no update was available. So I plugged it into my computer and a window popped up saying that an update was required in order to sync my phone with my computer. I clicked "download" and after a few minutes, "install." But the update failed. I tried restoring my phone and it failed--something about it could not access the server.
So, I begrudgingly went through the process to join the public beta test for iOS 12, downloaded the software and I still have the annoying pop-up message that everyone was talking about in the first place. However, I started getting it while running iOS 11.4.1! I hope they fix it soon!