This update fixes some WiFi, Bluetooth, and iPhone XS charging bugs; but, the best fix is this, documented by John Voorhees at MacStories:
iOS 12.0.1 includes a small design change on the iPad too. With the iOS 12 update, the ‘.?123’ key was moved. With version 12.0.1, that key has been restored to its previous position on the software keyboard.
For the first few days of running the iOS 12 beta, I didn’t notice this change. I did, however, notice the effects of this change. I couldn’t work out why I was suddenly inserting a lot more emoji into anything I was writing on my iPad until I looked at an old screenshot and figured out that the key for symbols and punctuation had been swapped with the emoji key. Presumably, this was changed for consistency with the 12.9-inch iPad Pro, but it upset seven years of iPad typing muscle memory.
Anyway, now that’s fixed and I can delete from my still-in-progress iOS 12 review the three paragraphs I spent pointing out what a terrible change this was.