I would like to prohibit cloud function from accessing to the Internet(e.g. http request).

It seems that you can achieve it by using Serverless VPC Access connector and “Route all traffic through the VPC connector” settings, but I’m not sure.

I don’t have much experience of cloud infrastructure and am a newbie of GCP.

I really appreciate it if you give me any advice.

I read GCP documents.
https://cloud.google.com/functions/docs/networking/network-settings?hl=en