You can install Google Play Services as a sandboxed app on GrapheneOS. That's not the issue. I believe the issue is that Google will use hardware attestation to check if the OS you're running it on is Google-approved.
I was surprised to find that this doesn’t work at all.
For instance, 300 is considered a valid IP by e.g. Firefox, typing 300/ into Firefox will navigate to http://0.0.1.44/.
I was expecting this to be interpreted as just Σ 256ⁿ × dₙ mod 256⁴. But it isn’t, Firefox won’t accept this (it performs a web search instead). Neither will curl (which tries to look up a domain by this name).
You can install Google Play Services as a sandboxed app on GrapheneOS. That's not the issue. I believe the issue is that Google will use hardware attestation to check if the OS you're running it on is Google-approved.