android system safety core

Magic I'm assuming the notification is coming from the Play Store.

Which version of GrapheneOS is your end-of-life device running?

Some discussion here:
https://www.reddit.com/r/antivirus/comments/1gpdhwz/guys_help_some_app_called_android_system/

Looks like it Powers sensitive content warnings in Google Messages

Take a look at this: https://developers.google.com/android/binary_transparency/google1p/overview
aaand this https://security.googleblog.com/2024/10/5-new-protections-on-google-messages.html
it's basically some on device machine learning resources for messages by google to detect spam and adult content.
Entirely up to you to install it. Likely you have messages installed and that's why play services is prompting you to install it.

How to check for and remove?

imp667 you can check your installed apps in play store and uninstall it
since its not something that will ever be bundled with Graphene you are free to uninstall it if at all its already installed