GrapheneOS is a great OS, and is currently a great options for a daily driver. One problem with them is that Graphene is still ultimately based on Android, which means they are reliant on Google playing ball with them as least a little, which makes it perhaps not a good long-term solution.

The other issue is that GrapheneOS is completely reliant on manufacturer updates to support a device. Once a manufacturer drops support for a phone, GrapheneOS must also drop support, as they can no longer provide security updates due to the hardware using proprietary blobs for its drivers.

PostmarketOS on the other hand can support a phone for potentially decades since it uses open-source drivers directly from the upstream linux kernel. That has the potential to drastically reduce planned obsolescence in phones.

I say the above as a GrapheneOS user, since PostmarketOS is generally not ready as a daily driver for the average person, hence why I suggest we support it so it can be polished and support for more phones added.