The watchOS update notes simply state that 4.3.2 "includes improvements and bug fixes". On the iPhone X, it's a relatively small file at just 252.2 MB.
USB Restricted Mode was first noticed by security researchers ElcomSoft back in May during the beta of iOS 11.4, when it was discovered to automatically password-lock an iPhone's or iPad's Lightning port after seven days of inactivity. That update brought Messages in the Cloud, after a long delay and stereo pairing for the HomePod. The official change-log from Apple also points to improvements in the reliability of Find My AirPods and syncing of mail, contacts, and notes with Exchange accounts.
Open Settings on your iOS device.
Tap on General and then Software Update. If you own a HomePod, it will automatically update itself to the latest software release without any user intervention.
iOS will prompt you when the update is ready to install. What is perhaps most surprising about iOS 11 is that even now, almost a year after the software was first released, there are still new problems that pop up left and right with the release of each new update. iOS 11.4 is the latest mobile software release from Apple, and users have flooded social media and Apple's support forums with complaints that their iPhone battery life has been decimated by Apple's most recent software update. After almost a year of dealing with buggy iPhones and iPads, iOS 12 is already a breath of fresh air in is current beta state.
In addition to appearing in the finished version of iOS 11.4.1, it's also available in the current beta versions of iOS 12. Like the iOS update, they both cite fixing bugs and improving stability.