Yes, please use the “Username + SSH Key” credential type as described here: 10 Scanning a System — Greenbone Enterprise Appliance 22.04.14 documentation
The uploaded private key must be supplied either in PKCS#8 format or base64 encoded. I’m still investigating whether we support both X.509 and OpenSSH formats. We will update our manual accordingly with the results.
The “Client Certificate” credential type looks to be a leftover from old functionality. We will investigate here too to see whether we can deprecate it.