I’m not a GrapheneOS user (yet). However, as I understand it GrapheneOS does not obligate the installation of “Google Play Services” but does permit the installation of the service in a sandboxed environment (or separate profile).

I think microG will work; it connects to the core Play Services API

As I understood, they will roll this out through “Google Play Services” and not the Android OS. So, any device with Google Play Services will be affected.

You can read more here: https://github.com/keepandroidopen/keepandroidopen.github.io/blob/main/src/content/pages/en/index.md