Google Cloud External IP Charges for Free Tier

Have a look at the documentation Google Cloud Free Tier section Always Free usage limits:

Google Cloud Free Tier is also available for external IP addresses that are being used by VM instances. In-use external IP addresses are available without additional cost until you have used a number of hours equal to the total hours in the current month. Usage calculations are combined across all in-use external IP addresses. Google Cloud Free Tier for in-use external IP addresses applies to all instance types, not just f1-micro instances.

and at the end of the page you can see when it was updated:

Last updated 2020-03-24.

As you can see, there's no changes for Always Free tier at the moment.

If some usage limits will be changed in the future you'll be informed in advance via official channel and documentation will be updated as well.

In addition, you can contact Google Cloud Support and use Basic support plan that available for free to ask any Billing related questions:

Billing support and read-only access to break/fix cases

Google updated their policy as of 2021-02-04. https://cloud.google.com/free/docs/gcp-free-tier#always-free-usage-limits

Google Cloud Free Tier does not include external IP addresses.