For desktops/laptops your best bet is https://libreboot.org/ the fastest one you can get is an i5 Thinkpad T480. Ideally flashed by yourself and all that.

https://system76.com/ for modern computers. Coreboot firmware with ME_cleaner, but with weaker ME disabling guarantees than libreboot. I wouldn't put my most sensitive stuff on these, but a great use case for something like QubesOS where you need lots of threads to maintain performance.

Phones are mostly a lost cause until we can get free and open source firmware SoCs. GrapheneOS has great privacy guarantees on a software side, but the Titan chip is a major black box, same with the modem and the SoC as a whole.