who can teach me to prepare ubuntu for ssh root access by putty in gcloud VM

i created a VM in google cloud through gcloud console with Ubuntu18

i can connect to root SSH through gcloud console web-based SSH

but i can not access this server by putty in windows

i created ssh keys and config all based on google help documents and did all correct, but i can not connect to that server

Port 22 is open in gcloud firewall rule

i edited ssh_config file and add permitrootlogin without-password

but i still can not connect to ssh by putty

Although when i input server ip in putty and click on Open, then terminal window open and ask for username. but when i enter any username such as root then i get error such as this : "publickey"

i did config centos7 VM hardly and now i can connect that by putyy without any problem

but NOT for ubuntu18

now i want to know that how i can connect to this server through ssh by putty

Google Cloud Platform 리눅스 시스템 관리인 우분투(Ubuntu)

프로젝트 ID: #17877511

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