Consider this: % swift demangle _$s9MetricKit10mxSignpost_3dso3log4name10signpostID__ySo03os_H7_type_ta_SVSo03OS_j1_F0Cs12StaticStringV0J0010OSSignpostI0VALSays7CVarArg_pGtF MetricKit.mxSignpost(_: __C.os_signpost_type_t, dso: Swift.UnsafeRawPointer, log: __C.OS_os_log, name: Swift.StaticString, signpostID: os.OSSignpostID, _: Swift.StaticString, _: [Swift.CVarArg]) -> () So, the problematic symbol is mxSignpost(…). According to the documentation, that’s available on iOS 13 and later. However, that’s clearly not the case O-: I see two possibilities here: The availability annotation is just wrong. The symbol is available on older system, but it moved, and the corresponding .tbd file doesn’t record that move. I suspect that it’s the latter [1] but, either way, it’s a bug in the MetricKit framework interface and you should file it as such. Please post your bug number, just for the record. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = eskimo + 1 + @