Connection from GCP Standard OR flexible Application Engine

For the LIFE of me there is nothing out there about connecting from a Standard OR flexible Google GCP App engine ?

Atlas can be reached from a Standard app engine using older driver 3.4 or less - java /or node … BUT that was 2018

I think ONLY a google Flexible (non free tier) app engine can reach Atlas mongodb … is this true ? we are using the latest streams driver for java for java based google GCP hosted App.

ANYONE know anything… it seems so obvious… but so little documentation on why not… my java GCP App on standard engine just returns objects… no errors… SEEMS to connect ok via the driver BUT cant insert documents OR read from… even changethe string to bas password… ZIPPO expceptions… and even opened up standard engine firewall … to no avail… for 27017

IMO this should work - in my mongodb world talk in 2019 I used Google App Engine’s free tier with the Node driver to build a web and mobile app. It was really easy to get set up, no issues. I had to look back at my notes from the talk, but basically I had everything default (standard runtime, us Central), I set up my Atlas instance on GCP also in the free tier us central region, created database user via Atlas UI, set IP access list in Atlas UI, set client connection URI in app.yaml file, and was off to the races.