okay, this was weird one.
I managed to fix it, but there is a much more pressing issue, which is that the database you would configure for production is somewhat useless.
The fix was simple, I changed the port in my ./config/database.js file from 5433 to 5432.
As I keep noticing, these issues didn’t exist for Strapi 3.x.x
Whilst my deployment of Strapi V4 has a ./config/env/production/database.js file, which doesn’t require a port as GAE use instance name, it still looks for a port, and I guess the only file the port was in is ./config/database.js file.
This begs the question, what is the ./config/env/production/database.js file doing, and do we now need to set up a port? is it really working?
If this is the case, then the only port number that works is 5432, which raises bunch of more concerns.
Been looking around the community a lot and V4 is not well supported compared to V3, the community is struggling to get common functionality that worked previously on V3 working on V4.
Hope this helps anyone else in the future!