If you are serious enough about security and privacy to use Graphene on your device, and you are willing to use Linux, you should at least look at using Qubes.
Try Qubes on a 2nd-hand Thinkpad, with Coreboot and ME_cleaner.
Plenty of discussion on https://forum.qubes-os.org/, including a hardware compatibility list (HCL) and a responsive community.
Caveats:
- Flashing the bios isn't always easy. It took me a while, but I got it working and I am not remotely technical. Research it.
- Buy something with lots of RAM. Its RAM hungry.
- Its not as easy as standard Linux/Mac/Windows: Qubes is rough around the edges sometimes, a learning curve, sometimes clunky. But still its pretty good since v4.2.
- Some software just doesn't run on it. Its not just a Linux thing, could be a RAM thing. E.g. some CAD programs. Dual boot (check that it can) or keep a spare 2nd-hand laptop on hand.
But its all really manageable and you get something that's a lot more safe than a standard computer.
My threat model is mostly just 'hackers' and corporations, so its probably overkill for me, but I wouldn't do anything important (e.g. banking, shopping) on anything else - that is until I started using GOS as well.