Nope. ptrauth needs a good hash in Hardware. There's only crc32c, aes, sha1 (-160) and sha256 (i.e. sha2-256). Of these crc32c is entirely insecure, aes not applicable, so we are left with AMD, Intel laptops (Goldmont), armv8 and Power8. For sure we don't care about any SHA vulnerabilities here, only about speed.

Blake2 is about a factor of 1000 slower. Secure hashes are not really applicable for pointer hashing (i.e. 48bit). Some need 16byte alignment (but you can use a stack word for that), some need excessive padding. Here the padding will kill you.

SHA3 is designed to be quite fast in hardware, there just isn't much hardware that accelerates it yet. Blake2 is faster in software, but that software is (as you note) much slower than SHA2's hardware implementations. So for existing systems SHA2 is the best option. Eventually SHA3 will probably be widespread and SHAKE128 with appropriately chosen output size will be the best choice.

SHA2 is by far not the best option for ptrauth. The best option is HW and API dependant. There are dozens of better options. I recently included most secure hashes with tons of variants into https://github.com/rurban/smhasher/blob/master/README.md#smh... SHA3 would be atrocious. Something like fletcher2 or wyhash seem to be best.