You should search for the many times where GrapheneOS has stated they won't work with Fairphone
Yep. Gos isn't the only mfg in town if you have or want a fairphone.
https://wiki.postmarketos.org/wiki/Fairphone_(Gen._6)_(fairp...
Given the state of Fairphone hardware, software and business, it is not surprising.
It's because Fairphone doesn't fulfil GOS's hardware requirements. If Fairphone addresses that, there's no reason for GOS to not support a Fairphone device.