The GrapheneOS developers had this to say about Fairphone back in 2021:
“It's not possible for GrapheneOS to support @Fairphone devices because they're far from meeting even the most basic security requirements. They haven't come close and it doesn't appear to be a priority for them.“
I also would love a Fairphone-like device running GrapheneOS, but I don’t think Fairphone is going to be the company to deliver to GrapheneOS’s high standards.