I have good news! There is an open pr (thanks @kvch!) to proper update functionbeat to go 1.16.
There is another solution we announced recently that could bypass functionbeat altogether, that is using GCP Dataflow to forward logs to Elasticsearch. You can read more in this announcement blog post. With it you can route logs to GCP Pub/Sub and then forward them to your public routable Elasticsearch cluster with a GCP Dataflow Job.
I worked on a Terraform based example for GCP Audit logs, you may want to check that out too.