The hardware capability that GrapheneOS loves to use as a shield to deny support for other devices is the ability to use custom AVB keys. Without custom keys you can't relock the bootloader after installing a custom OS on most phones. The consequences of having an unlocked bootloader are that you are susceptible to an evil maid attack.

This is a real threat, but the reality is that the average person is more likely to be hacked/spied on from the software side, which Graphene would protect you from as effectively as it does on Pixel.