Disconnected: No Supported Authentication methods available(Server sent: publickey,gssapi-keyex,gssapi-with-mic). when connecting to ORACLE Cloud Instance with PuTTY or MobaXterm.

The problem.

The downloaded private key is not in RSA format. Open the file in notepad.You should see something like

-----BEGIN PRIVATE KEY-----

MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgw

.....

cC8HzXh8lbx9iPgYP4i3dsGH

-----END PRIVATE KEY-----

The solution.

Convert the key.

openssl rsa -in ora_cloud.key -out ora_cloud_rsa.key

Result.

-----BEGIN RSA PRIVATE KEY-----

MIIEpAIBAAKCAQEAsCELMYDk8VCo0tAs4dG9vr5w

.....

cVdJXikv+d6JpSQAB3g4o/hyERO/v3AvB814fJW8

-----END RSA PRIVATE KEY-----

Use the new rsa key file.