I am confused. I thought that apps compiled with Xcode 27 (and with a 26 target) for iPhone only would show black bars on eithr side on iPhone Duo. Am I mistaken. See this video for more context.

With Xcode 27.0, apps are expected to support resizing, so they resize the app, but still in compatibility mode. Targeting previous SDKs, you will get the centered result.

I sorted it out. I compiled the app using Xcode 26 and then installed in in DeviceHub for the duo and I got what I was looking for.

Is it still possible to use two apps in that compatibility mode?

No, this is exactly what is supposed to happen. Black bars are for apps compiled with Xcode 26

Did you drop back to a different Xcode/SDKs? Think it's compiled SDK version, not target OS.

I compiled the app using Xcode 27 and then located the compiled app in the container. I then used terminal to install it in DeviceHub for the iPhone DUO. I never compiled it with Xcode 27.1 at all. Does that make sense or am I missing something?

I'm thinking that the issue is only present for folks that compiled with Xcode 26.x or older, and haven't build against a Xcode 27.x SDK. Downloading myself right now. For science.

Looks confirmed, same app. Just different Xcode versions. Both are minOS 26.0

wait duo still letterboxes a 26-target iphone app?

This is fixed if you compile the app with Xcode 27.1. You do not need to change the target. Just build under Xcode 27.1 and resubmit your app when allowed.

As long as you compile with Xcode 27, you are compiling with the latest SDK, hence no black bars. If you want black bars compile with Xcode 26