I think the Raspberry PI is awesome, but it is a big pile of closed source processing units that no-one completely understands. For example it boots from the GPU, not the CPU. Wow...
I understand why they stopped working on the Pi, but I don't necessarily agree with the reasons.
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.
I would use an "open as possible" hardware platform like those from Bunnie https://www.bunniestudios.com/blog/?cat=28 for example.
Novena Laptop https://www.crowdsupply.com/sutajio-kosagi/novena