dc32f0cfe84def651e0e I am unaware of an organized list of determined-to-be-deficient devices (let alone with reasons for each device). Given the number of Android phones that are shipped each year, keeping such a list up to date would be difficult, and it's not clear it would be valuable.
People often inquire about Fairphone support, so I think there a lot of threads mentioning that. And I think there are a lot of threads discussing MediaTek devices. So these web searches might be fruitful:
site:discuss.grapheneos.org fairphone
site:discuss.grapheneos.org mediatek
I don't think the GrapheneOS team is overlooking any devices that meet the requirements in that FAQ entry.