what's the purpose of passphrase in hybrid cryptography? What's the purpose of a passphrase in hybrid cryptography? can it actually be used for authentication or if i put in another signature algorithm will it be like, two authentications?
Some systems like SSH will use passphrases to control the use of private keys: instead of storing the private key unencrypted on disk it's stored encrypted (symmetrically) by a key derived from a passphrase. That ensures that only an authorized user can use the SSH key pair to access a remote system.
There's no requirement for passphrases in hybrid cryptography in general. EG TLS doesn't use passphrases and involves hybrid cryptography (asymmetric key exchange + symmetric encryption).