gomboc I did read that but I found it a bit vague.
I'm not quite sure how to help. The original question was "If I give it all permissions, will it function exactly the way it does in stock android?" and I believe the material on the web site makes it clear that's not the case. What's on the web site clearly states that on GrapheneOS Google Play does not operate outside the Android app sandbox.
gomboc I don't know if the developers ever respond on this forum but it'd be good to get a bit more detail from them.
The developers absolutely do respond on this forum. Reading forum posts for a while may well demonstrate that. That said, they spend most of their time developing, as opposed to responding to forum posts.
When there are specific questions about Google Play on GrapheneOS, various people answer them. A web search for site:discuss.grapheneos.org sandboxed will likely turn up some questions and answers.