Just in case someone else runs into this issue (UE4.27) I spent some time debugging into UnrealBuildTool, something is a miss with how the TargetRules, MacToolChainOptions and GlobalCompileEnvironment are getting generated, culminating in line 1504 of MacToolChain.cs returning before dSym’s are requested to be built, but the dSyms are still added to the BuildProducts list that gets added to the manifest.
Not sure what the actual fix or cause of this is, but adding this to your Editor.Target.cs will allow you to build, but you will not have dSyms
if (Target.Platform == UnrealTargetPlatform.Mac)
{
bOmitPCDebugInfoInDevelopment = true; //Attempt to fix Mac dSym issues
}