try using publicHeadersPath

Author: russellwheatley

Package.swift

@@ -30,9 +30,10 @@ let package = Package(
         .product(name: "FirebaseInstallations", package: "firebase-ios-sdk"),
       ],
       path: "packages/firebase_core/firebase_core/ios/firebase_core/Sources", // Specify the path to the source files
-      resources: [
-        .process("packages/firebase_core/firebase_core/ios/firebase_core/Sources/firebase_core/Resources"),
-      ],
+      publicHeadersPath: "packages/firebase_core/firebase_core/ios/firebase_core/Sources/firebase_core/include/firebase_core",
+      // resources: [
+      //   .process("packages/firebase_core/firebase_core/ios/firebase_core/Sources/firebase_core/Resources"),
+      // ],
       cSettings: [
         .headerSearchPath("packages/firebase_core/firebase_core/ios/firebase_core/Sources/firebase_core/include/firebase_core"),
         .define("LIBRARY_VERSION", to: "\"\(library_version)\""),