Your "development build" is another person's daily driver.

Case in point: GrapheneOS (or any other custom Android distro) is unlikely to be able to ever pass remote attestation, even a signed, secure boot build with the bootloader relocked, because it's not the original OS for the hardware.

Same goes for any desktop Linux.

GrapheneOS implements its own attestation so you can attest that it's real GrapheneOS. The valid approach they've chosen is to try and get on a level playing field with the big guys rather than destroy the playing field. They have a good argument their OS is very secure, so you should accept its attestation. This is how a user-friendly OS backdoors into the attestation system.

I still think destroying the playing field is better, but less likely to succeed.