I tried it, Graphene isn't really a good alternative because the built in apps are so bad that you end up needing to install the Pixel/Google versions anyway.
If I have to install Google Messages for RCS, Google Calendar, Google Contacts, Pixel Camera (which forces you to use Google Photos for basic functionality), … where is the benefit?
If I have to turn Graphene into a Pixel to make it usable, and I did, there’s not much point. And the apps are 90% of the time very noticeably better on iOS, so overall turns into a very bad trade.
You still get much better privacy with GrapheneOS even if you install Google apps since they are sandboxed; they don't have access to unique device identifiers and you can control what Google can access by adjusting its permissions, as opposed to having full reign to do whatever it wants. Also you don't have to use all the Google apps, plenty of open source and/or privacy respecting alternatives out there. Pixel Camera only needs Google Photos for the photo previewer, everything else works without it or you can install gcam services provider to use any gallery you want