Looking at the home screens, the primary difference you'll find is that in iOS 26 the background of the dock and the search option that sits in between the dock and the home screen icons are more transparent and have a sheen to the edges, whereas in iOS 18, these are slightly darker.

At WWDC 2025, Apple revealed a major visual shake-up for iOS (not to mention the rest of the company’s operating systems). This is the biggest change, aesthetically, since the shift away from the stitching,

You can create custom backgrounds for messages in iOS 26. - Apple / Mashable Photo Composite Apple released the public beta for iOS 26 today. However, you probably shouldn't install it without a plan.