Same issue here, also posted: FB13946288

Just tested with the new beta. This is working as of iOS 18 beta 3.

Getting an different error than I've seen reported here in both Xcode 16.0 and 16.1 beta 2 (without Legacy Previews): "Cannot preview in this file. Implicitly unwrapped nil value in GeneratedAssetSymbols.swift" I've performed the reporting requested and submitted a feedback: FB15176682