I also had this problem, login from putty as root was fine but from the non-root user gave me the error above. I tried the methods given in the link but it didn’t help, eventually I managed to do it by following this guide: https://www.vultr.com/docs/using-your-ssh-key-to-login-to-non-root-users

This: “No supported authentication methods available (server sent: publickey)” happened to me after I turned on Microsoft One Drive backup and sync for my files including the directory where I save my ssh key. In my case the solution is simple: just go to Putty => SSH => Auth and just (re)browse again to my same key and save, then it worked. It looks backup and sync software such as Microsoft One Drive (and may be the same with Google Drive), affect the way Putty sees and identifies directories if the key directory is specified then later installing or turning on backup and sync including that directory.

@thelunchbawx

The public key generated by puttygen cannot be used directly on Ubuntu you need to change its format as mentioned here

Hope this helps

@thelunchbawx, I am having the exact same problem. Did you figure out a solution?

In my case, I removed default login name from putty and it worked

Hi,
I resolved this by using PuTYY Generator.
Click Conversion/Import key from the menu
Then select the private key generated previously from the terminal and finally save the new private key.
I used this new generated private key to connect via SSH using putty to the droplet and it works for me.