I am having the same issue on both of my machines (both running Xcode 26.4 and 26.4 simulators.) After setting the simulator back to iOS 26.2, I can work in the SwiftUI canvas.

In 2026 this is still a massive issue. No TestFlight emails are being sent at the moment.

I'm having the same issue here in 2025. I have to download and install Swift packages locally in each project because the ssh handshake fails. I work on enterprise apps so this is beyond tedious.