Have you installed google services on your phone? they are available through the grapheneOS official "App Store" app. This should be installed before whatsapp is installed (at least that is the instruction for general apps depending on google services).
Perhaps you have done so already, but just a general advice: when using google services and invasive apps like WhatsApp, it can be a good idea to install in their dedicated profile and allow the notifications to pipe through to your main profile instead of installing both in your main profile. If you need help configuring it, let me know.