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.

With the introduction of OS version 26, Apple streamlined the user interface across iOS, iPadOS, macOS, watchOS, tvOS, and visionOS. Liquid Glass is now the company’s universal design language, borrowing cues from the Vision Pro’s operating system and preparing for a future dominated by mixed-reality gadgets.

Indeed, Liquid Glass does bring somewhat of a major change to iOS 26, or what we would have called iOS 18 (Apple is switching iOS numbers to years, and iOS 26 will release in the fall). I've been using the developer beta of iOS 26 for some weeks now,