This is from 2023, but this might still be a good read on how to get to a very low watt idle build, there’s a few more post on other older builds on that blog as well: https://mattgadient.com/7-watts-idle-on-intel-12th-13th-gen-the-foundation-for-building-a-low-power-server-nas/

None basically. There’s a Sony phone has LineageOS (including +microg variant) support, but it’s not ideal either.

If you are open to building something yourself this might be an alternative (disclaimer: I just know of this project but no idea how well it works): https://www.findmycat.io/