After I added following lines to the /etc/ssh/sshd_config for sftp setup as online guide suggested.
Match group sftp ChrootDirectory /home X11Forwarding no AllowTcpForwarding no ForceCommand internal-sftp
I can not open ssh to instance with "This service allows sftp connections only" message.
I guess ForceCommand internal-sftp limits ssh connection.
It's dummy that I blocked myself.. Is there way to fix this problem without lossing instance data? Any help will be highly appreciated. (Pics are captured from my gcp-cloudshell)