When creating a credential in CCS using an OpenSSH certificate, you get the following error:
A valid certificate file was not present at the given path. Make sure that the certificate file path is a valid Putty Private key file
CCS 12.6.x
By default, when you create or convert a key to OpenSSH, the file does not have a file extension. CCS 12.6.1 is expecting the file to have a .ppk extension.
Only in 12.6.1 with SCU 2023-2, you need to manually add the .ppk extension to the file for CCS to accept it.
NOTE: This is changed in CCS 12.7 as in 12.7 only OpenSSH keys are accepted, so the OpenSSH files will no longer need the .ppk extension manually added.
Additional KB for creating or converting OpenSSH credentials:
Configuring certificate-based credentials in CCS for UNIX platform