How can a Google Cloud Build private pool worker can reach out to a service across a vpc peering?

Question

We use cloud build to run the migration step of our app among other things. Recently we have decided to migrate the database to a third party that offers a VPC peering option to connect to the database.

I have tested the migration steps successfully in a VM multiple times without problem. The final step would be a redeploy of the app to run a specific database migration.

Here is when I noticed Cloud Build is unable to reach the service.

Reading the documentation for Cloud Build points me to having a private pool of workers attached to the VPC.

I create the worker, assign the VPC without any specific IP range and the third party is still unreachable. I recreate the worker with a IP range within the VPC and it is still unreachable.

Adding a debug step for the network (traceroute) shows the network request completely stopping at the docker network adapter ip 192.168.10.1.

My VPC is very vanilla, there are no special rules besides the peering and maybe one or two services at most but no special egress/ingress rules are present. The assigned range to the worker is 10.0.0.0/16.

What am I missing here?

I have tried to create private workers with different IP assignments, using different service accounts and granting them high privilege permissions.