In Xcode 12, created a small universal app. The app "Get Info" shows two checkboxes: "Stationery pad" and "Locked", but not "Open using Rosetta", which I need.
I verified that the binary is universal (has two architectures: x86_64 and arm64).
Is there a hidden option or a info.plist flag I must enable for that?
You will need to build with this Property List Key LSRequiresNativeExecution disabled.
An excerpt from the Apple Documentaion:
... this key prevents the system from using the Rosetta translation process to execute the Intel portion of a universal app on Apple silicon.
arch -x86_64 /path/to/program