SSL Pinning security: can MitM generate the same public key?
It's astonishingly difficult.

With RSA, it's literally a mathematical impossibility.

With Weierstrass, Montgomery and Edwards elliptic curves, the possibility of generating the same public key from different private key should be impossible assuming the private key scalar value doesn't overflow the order of the generator of the group.

With Hash-based digital signatures, this may be possible, because the public key is the tree hash of many one-time hash signature public keys. But still, finding such public key collision is as difficult as finding any regular hash collision. (not to mention real-world hash signatures often use randomized hashing).

Lattice-based schemes have the mathematical possibility of generating colliding public keys if the public component reduces the dimension of the private component, but that's very improbable. However, it should be noted, even the public component are randomly generated in most candidate schemes in NIST Post-Quantum Cryptography Project.