HeadyTrichs As mentioned the notification to which you refer is for when you have sandboxed Play Services installed. That is both the services and store from the GrapheneOS App Store app.
When you do and when you've provided it the necessary exceptions to battery optimisation etc as outlined here:
https://grapheneos.org/usage#sandboxed-google-play-installation
Then you will see the notification sitting in the notification shade as a silent notification which can be tapped and various Play settings can be changed.