On Mac, it might be caused by a version mismatch. I’m on macOS Tahoe 26, and once I updated the Command Line Tools, Xcode, and Metal Toolchain to the latest version, I got the same error.
Look at: /Users/Shared/Epic Games/UE_5.6/Engine/Config/Apple/Apple_SDK.json
There are Main, Min, and Max versions defined. Changing “MaxVersion” to “26.1.0” solved it for me.