How to migrate macOS keychain entry to new rewritten app?

I'm working on replacing an AppKit-based Mac app with one built on Catalyst, and the Catalyst app doesn't seem to be able to read the keychain item that was saved by the old app.

Both apps are using the same bundle ID. The old app uses the old SecKeychain APIs - SecKeychainFindGenericPassword and friends - and the Catalyst app uses the newer SecItemCopyMatching and such. When I try using the new API in the old app to search for the entry, it works, but the exact same code in Catalyst fails.

Here's how I save an item in the old app:

NSString *strItemId = @"my_item_id;

NSString *username = @"user";
const char *userPointer = [username UTF8String];

NSString *password = @"password";
const char *pwPointer = [password UTF8String];

SecKeychainItemRef ref = NULL;
OSStatus status = SecKeychainFindGenericPassword(0, (UInt32)strlen(strItemId.UTF8String), strItemId.UTF8String, 0, NULL, NULL, NULL, &ref);

if (status == errSecSuccess && ref != NULL)
{
    //update existing item
    SecKeychainAttribute attr;
    attr.length = (UInt32)strlen(userPointer);
    attr.data = (void *)userPointer;
    attr.tag = kSecAccountItemAttr;
    
    SecKeychainAttributeList list;
    list.count = 1;
    list.attr = &attr;
    
    OSStatus writeStatus = SecKeychainItemModifyAttributesAndData(ref, &list, (UInt32)strlen(pwPointer), pwPointer);
}
else
{
    status = SecKeychainAddGenericPassword(NULL, (UInt32)strlen(strItemId.UTF8String), strItemId.UTF8String, (UInt32)strlen(userPointer), userPointer, (UInt32)strlen(pwPointer), pwPointer, NULL);
}

And here's the query code that works in the old app but returns errSecItemNotFound in Catalyst:

NSMutableDictionary *queryDict = [[[NSMutableDictionary alloc]init]autorelease];
[queryDict setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];

[queryDict setObject:(@"my_item_id") forKey:(__bridge id)kSecAttrService];

[queryDict setObject:(__bridge id)kSecMatchLimitOne forKey:(__bridge id)kSecMatchLimit];
[queryDict setObject:(__bridge id)kCFBooleanTrue forKey:(__bridge id)kSecReturnAttributes];

CFMutableDictionaryRef outDictionary = nil;
OSStatus err = SecItemCopyMatching((__bridge CFDictionaryRef)queryDict, (CFTypeRef *)&outDictionary);

I tried creating a new blank AppKit-based Mac app project in Xcode and gave it the old Mac app's bundle ID, and the SecItemCopyMatching query code above works there. Then I created a new iOS target with Catalyst enabled, also with the same bundle ID, and the query code running there under Catalyst returned errSecItemNotFound. So maybe the issue is something specific to Catalyst?

Is there something I need to do with the Catalyst app to give it access to the old app's keychain entry, besides setting its bundle ID to match the old app?