Firewall settings work just fine for our platinum clients with complex network architectures, I don't see why it wouldn't in your case unless something was misconfigured.
Normally I'd think I had configured something wrong, except in this case it was insanely simple. A network label that allows all ports both ingress and egress, to any destination/source, definitely applied to the servers, and yet they had constant connection issues with each other.
It probably was something I did, but the combination of those issues, surprise egress bills, very laggy UI, and various other little niggles just made it not worth my time for now. I'm keen to avoid vendor lock-in anyway, so GCP and AWS don't have that many extra features over smaller providers for me.
And I would have been totally fucked over by that Postgres connection limit when we went into production, I'm glad I dodged that bullet! I hadn't bumped into that when playing with dev environments, and I haven't seen that limit mentioned anywhere.