Can't connect to SFTP and SSH (Google Cloud Platform)

I recently updated ubuntu to 20.04 and since then I can't connect to VPS via SSH or SFTP. I was trying to use different apps: Filezilla, WinSCP, Bitvise SSH but none of those can't connect to VPS. I thought that I have to set external IP to static but nothing has changed. I checked my firewall and it has default-allow-ssh rule set to all targets for 22 port. I also connect with 22 port and correct external IP and PuTTY private key. I was restarting VPS a lot of times but it's not working. Ask me for more details if needed. When I was trying to log in this error occures.

First of all, as you mentioned before, your VM needs to have an external IP address, in order to send/receive external connections.

Then, you would be able to connect it using tools like putty or another tools, here is the documentation about it[2].

My recommendation is try first by shh directly on your GCP console, and then try external.