I have made a topic regarding that:
Best would be buying Talos|| full or minimal:
advantages:
- Power9 CPU which is an open source CPU (sorta)
- OpenBMC no ME or PSP
- no nonfree firmware/blobs or DRM
Disadvantages:
- No laptops only Desktop/Workstation
- Incompatible with Xen/Qubes
- Unknown GPU compatibility/performance (i didnt research that but you can do it if you want GPU)
Other CPUs like Intel or ARM or AMD they are into controversial state which one is more shittier than the other but all of them shit (intel on the top of the list).
If you want to buy a laptop well there are many here for e.g certified PCs with Qubes: (all of them either Intel or AMD)
… and many others
These options use open source BIOS called corebot (not fully free software) better than the full proprietary BIOSs you see in the markets.
if you want cheap old with free software BIOS called libreboot check certified from FSF here is the list:
https://ryf.fsf.org/categories/laptops
Note: No blobs included thats mean no updates for microcode