The FBI don’t need a back door, they just to find the plaintext default password some unpaid intern built into the product for testing purposes before Russia does.
I present Dual_EC_DRBG as a great example of "you can't trust shit"
But also CPUs and motherboards may be compromised too. Whether it's by China or the US.... It's a plausible thing. Intel IME and AMD Secure Processor amongst others...