Update: I scoured the source code of your project, including the source code downloaded by CocoaPods. The "GADNativeCustomTemplateAd" symbol that's causing problem is defined... nowhere. It is *declared* in Libraries/Plugins/iOS/GADUNativeCustomTemplateAd.h as an Objective-C property, and used as a return type in Libraries/Plugins/iOS/GADUNativeCustomTemplateAd.m and Libraries/Plugins/iOS/GADUAdLoader.m. But the *definition* for this object (i.e. the layout of its contents) appears nowhere.
For this reason I'm forced to the preliminary conclusion that your project must be bogus, and I can't see how Xcode could compile this successfully. Before giving a final assessment I'm going to try building it on Xcode, but I have to upgrade my macOS to Sonoma first for the required Xcode version to run (something I wanted to avoid, but that's another story). If Xcode can't build it, you'll need to look for the cause in your Unity project, it will not be the builder's fault. If it can, then I'll be quite stumped for I fail to see how a compiler can compile an object for which it's not given a detailed specification.
*edit* This is confirmed. Xcode itself cannot build your project.
% Xcode's build log
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:12:31: error: cannot find protocol declaration for 'GADRewardedAdDelegate'; did you mean 'GADNativeAdDelegate'?
@interface GADURewardedAd () <GADRewardedAdDelegate>
^~~~~~~~~~~~~~~~~~~~~
GADNativeAdDelegate
In module 'GoogleMobileAds' imported from /Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.h:5:
/Users/pmbaty/Library/Developer/Xcode/DerivedData/Unity-iPhone-fslpzlqfckrgoigrafrchegzovuh/Build/Intermediates.noindex/ArchiveIntermediates/Unity-iPhone/BuildProductsPath/Release-iphoneos/XCFrameworkIntermediates/Google-Mobile-Ads-SDK/GoogleMobileAds.framework/Headers/GADNativeAdDelegate.h:13:11: note: 'GADNativeAdDelegate' declared here
@protocol GADNativeAdDelegate <NSObject>
^
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:27:42: error: no visible @interface for 'GADRewardedAd' declares the selector 'initWithAdUnitID:'
_rewardedAd = [[GADRewardedAd alloc] initWithAdUnitID:adUnitID];
~~~~~~~~~~~~~~~~~~~~~ ^~~~~~~~~~~~~~~~
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:46:34: error: type-id cannot have a name
completionHandler:^(GADRequestError *_Nullable error) {
^~~~~~~~~~~~~~~
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:46:50: error: expected ')'
completionHandler:^(GADRequestError *_Nullable error) {
^
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:46:33: note: to match this '('
completionHandler:^(GADRequestError *_Nullable error) {
^
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:46:32: warning: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]
completionHandler:^(GADRequestError *_Nullable error) {
^
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:47:20: error: use of undeclared identifier 'error'
if (error) {
^
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:51:52: error: use of undeclared identifier 'error'
[error localizedDescription]];
^
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:45:20: error: no visible @interface for 'GADRewardedAd' declares the selector 'loadRequest:completionHandler:'
[self.rewardedAd loadRequest:request
~~~~~~~~~~~~~~~ ^~~~~~~~~~~~~~~~~~~
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:64:27: error: no visible @interface for 'GADRewardedAd' declares the selector 'isReady'
return [self.rewardedAd isReady];
~~~~~~~~~~~~~~~ ^~~~~~~
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:68:24: error: no visible @interface for 'GADRewardedAd' declares the selector 'isReady'
if ([self.rewardedAd isReady]) {
~~~~~~~~~~~~~~~ ^~~~~~~
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:70:22: error: no visible @interface for 'GADRewardedAd' declares the selector 'presentFromRootViewController:delegate:'
[self.rewardedAd presentFromRootViewController:unityController delegate:self];
~~~~~~~~~~~~~~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.m:77:39: warning: 'adNetworkClassName' is deprecated: Deprecated. Use loadedAdNetworkResponseInfo.adNetworkClassName instead. [-Wdeprecated-declarations]
return self.rewardedAd.responseInfo.adNetworkClassName;
^
In module 'GoogleMobileAds' imported from /Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.h:5:
/Users/pmbaty/Library/Developer/Xcode/DerivedData/Unity-iPhone-fslpzlqfckrgoigrafrchegzovuh/Build/Intermediates.noindex/ArchiveIntermediates/Unity-iPhone/BuildProductsPath/Release-iphoneos/XCFrameworkIntermediates/Google-Mobile-Ads-SDK/GoogleMobileAds.framework/Headers/GADResponseInfo.h:80:71: note: 'adNetworkClassName' has been explicitly marked deprecated here
@property(nonatomic, readonly, nullable) NSString *adNetworkClassName GAD_DEPRECATED_MSG_ATTRIBUTE(
^
In module 'GoogleMobileAds' imported from /Users/pmbaty/Desktop/JoshuaF-CocoaPodsGoogleAds/Libraries/Plugins/iOS/GADURewardedAd.h:5:
/Users/pmbaty/Library/Developer/Xcode/DerivedData/Unity-iPhone-fslpzlqfckrgoigrafrchegzovuh/Build/Intermediates.noindex/ArchiveIntermediates/Unity-iPhone/BuildProductsPath/Release-iphoneos/XCFrameworkIntermediates/Google-Mobile-Ads-SDK/GoogleMobileAds.framework/Headers/GoogleMobileAdsDefines.h:10:56: note: expanded from macro 'GAD_DEPRECATED_MSG_ATTRIBUTE'
#define GAD_DEPRECATED_MSG_ATTRIBUTE(s) __attribute__((deprecated(s)))
^
2 warnings and 10 errors generated.
%
I suggest you start over and redo the Google integration properly. If you're certain you did it right, then this release of your Google asset is bogus and you should file a bug report where it belongs.