SeaSaltIceCream This is not a GrapheneOS change, but rather an Android 13 one.
It means you installed an app manually or via an app store like F-Droid that doesn't utilize modern installation methods.
You can bypass that warning by following the steps here:
https://support.google.com/android/answer/12623953?hl=en
That said, I urge you to be careful about which apps you grant these extremely invasive permissions to.