Although I have assigned my public key to my gitLab account and used my private key. It still says "Exhausted available authentication methods". When I try to clone repository from gitlab.

When I cancel it, there are missing files in the cloned repo. (I can clone other repositories from my gitlab but only with thisone I experience the issue)
I would select "private key" and copy a private key generated without passphrase protection, to simplify the process.
Using a password (not passphrase) would mean using a username/password, which is not allowed for any Git remote repository hosting service (GitHub, GitLab, ...)