Swift Signing User in with Access Group not working

I don’t know how this could happen, but the string for the access group is wrong in your entitlements.

It should be $(AppIdentifierPrefix)com.wishlists-app.group instead of $(AppIdentifierPrefix)SN26HDFT24.com.wishlists-app.group.

Your extension must have the same app group and keychain group activated. I can’t see anything of your app extension. Then you must also call useUserAccessGroup("SN26HDFT24.com.wishlists-app.group") in your extension.