I've got several arm64 boards, and only one of them comes close to a "libre" boot. The Marvell Espressobin runs a fork of the Arm Trusted Firmware that diverged so far from mainline that after Marvell stopped working on it in 2018, it hasn't been touched, CVEs and all. The Pi actually has a chance of having a reimplemented bootloader and being used by a lot of people.