Getting charged for "E2 Instance Core running in Seoul" but there is no VM

I'm being charged for "E2 Instance Core running in Seoul". The billing report says the related service is "Compute Engine", but there is no VM instance running from Compute Engine. I can't track the cause of the bill.

Not sure if it's related, but I created 4 Cloud Run services with 0 minimum instances auto-scaling settings and runs probably 0~5 mins per day. But the usage of the "E2 Instance Core running in Seoul" is 84 hours for 7 days. So I don't think that's the cause.

Why am I being charged for "E2 Instance Core running in Seoul"?

As confirmed in the comments, when using a VPC Serverless Connector, this connector is charged as e2-micro instances as stated by pricing docs.

This is the reason why you see these charges even if you're not having a VM in GCE.

Also to confirm, you can use the following tip from the docs:

You can view your Serverless VPC Access costs in the Cloud Console by filtering your billing reports by the label key serverless-vpc-access.