Are you referencing to this documentation, where the logs severity available are INFO and ERROR? If so, this is intended behavior as of now.
https://cloud.google.com/appengine/docs/standard/nodejs/writing-application-logs
Would you require to have a console.debug() logged as Severity: Debug, same as the Python counterpart?
https://cloud.google.com/appengine/docs/standard/python/logs/#writing_application_logs
If so, this is a feature request which you would be able to file in the Public Issue Tracker as a feature request under the App Engine:
https://cloud.google.com/support/docs/issue-trackers
Here is the direct link:
https://issuetracker.google.com/issues/new?component=187191&template=1009600
As a workaround, you could try using the Node.js Packages logging library available for Google Cloud Platform Service APIs or using the Bunyan/Winston plugins.
Node.js Packages:
https://cloud.google.com/nodejs/docs/reference/logging/2.0.x/Log#debug
Bunyan/Winston:
https://cloud.google.com/logging/docs/setup/nodejs