Short description: AWS RDS connecting server to PgAdmin 4, PostgreSQL 11

Done: I have done similar to this guy or to this aws guide but at the end when I click save it does not accept it for me. instead gives the following

ERROR:

Error saving properties 
Unable to connect to server: 
timeout expired

What I have tried to solve the problem:

• The instance is active it is 2 hours after creation
• I have also allowed to access database with outside of AWS database client "YES"
• this stack overflow answer does not deliver results https://stackoverflow.com/a/37903485/10270590 actually after refreshing my security group like the guide says my whole database disappeared
• I have home wi-fi so there are no corporate firewalls or any of those issues https://serverfault.com/q/705312/535406
• while reading the pervious server fault post I looked up my
  • RDS/Databases: what was empty
  • RDS/Security groups: empty and I have this message:

Your account does not support the EC2-Classic Platform in this region. 
DB Security Groups are only needed when the EC2-Classic Platform is supported. 
Instead, use VPC Security Groups to control access to your DB Instances.

• I have tried which this question https://serverfault.com/questions/656079/unable-to-connect-to-public-postgresql-rds-instance that had 2 good answers but they gave the same error even after doing bot of the changes
  • https://serverfault.com/a/656119/535406
  • https://serverfault.com/a/880710/535406
• same as the above one - AWS RDS Database show timeout error