@rana It’s weird… Did you clear the previous RSA key and add your ed 25519 key (~/.ssh/id_ed25519.pub) to the Clear Linux VM instance? per your previous screenshot, you configured the RSA public key to the VM, but from the ssh log, it seems no corresponding RSA private key under ~/.ssh/ folder.
To ensure you have key setup properly on your Debian9 host, what if you create a Debian VM on GCP by following the step 13, but skip the 2nd and 3rd bullets of changing boot disk. That should create a Debian VM with your SSH key, and you could test whether you can login to it with the corresponding private key?