I use Gboard with the network permission disabled. It works well but I hope they have a better stock keyboard, I haven't found any others that don't annoy me in one way or another.
So if you're using Graphene for privacy from Google specifically, it's not safe to install things like Gboard even with the network permission disabled. Even if they don't use IPC in this way today, there's no telling what the Google-of-tomorrow will do.
This is true and even vastly understated. Google is like the Walter White of companies. Starts out innocent, turned into a monster, everyone around him astonished at the dark, depraved change.
So if one thinks "nah, Google wouldn't do that", I have a bridge to sell you...