Cant access GCP Compute Engine
Solution 1:
Probably, you need to apply GCP firewall rule to allow ingress connection on SSH port of that instance on the VPC network.
By default there is default ingress rule for allowing ssh in GCP. You can create firewall rules in GCP manually as well.
If your GCP VM instacne does not have external IP, make sure you are connected using either VPN, bastion host or Identity-Aware Proxy(IAP) for TCP forwarding.
You may need to allow ingress traffic from the IP range 35.235.240.0/20 in GCP firewall if you are using IAP to connect the instance. This IP range is used by IAP for TCP forwarding.