Xcode 12 Problems: "Build input file cannot be found "- Building for release on a react native app

Build for "Any iOS Device" (for example, "Archive" because you want to upload to AppStore):

• Delete arm64 from "Excluded Architectures"
• Delete x86_64 from VALID_ARCHS
• Add arm64 to VALID_ARCHS

All this changes on both "Build Settings", project and target. And if you want to build for simulator do the inverse path:

• Add arm64 to "Excluded Architectures"
• Delete arm64 from VALID_ARCHS
• Add x86_64 to VALID_ARCHS

That works for me.

So I had the exact same issue. After updating to Xcode 12 I had originally set both my project and target 's 'Excluded Architecture' to arm64 in order to run on Simulator. But, as you mention, that blocks anything from working on Release / Real device. All I had to do was switch to 'Any iOS Simulator SDK = arm64' instead of all of them, see screen shot below:

link to screenshot