Comment by RiverCrochet

Get off the short bus twin. CPU backdoors do no good unless there is cooperation with network driver code or the CPU itself has full operating system with a full network stack.

Intel's ME comes really close to that, but I don't think Intel's ME has drivers for every possible NIC and bus a NIC can appear on in its little Minix. So, just put a Broadcom NIC in a PCIe slot and leave the Intel onboard NIC empty, or LAN facing only.

Xiaomi may get Chinese 4G/5G baseband chip manufacturers to put in backdoors in Chinese phones, but they're not needed - the Chinese government pretty much already has total control of its Internet. For other countries, how are they going to make Qualcomm provide something undocumented CPU instructions can access.