How to grant Cloud9 access to IAM user without console login enabled

Hello.

I think you will need access to the management console to access Cloud9's IDE.
As far as I know, an IAM user who does not have access to the management console cannot open the Cloud9 IDE.
https://docs.aws.amazon.com/cloud9/latest/user-guide/open-environment.html

Although it is not a connection from Cloud9, you can edit files on EC2 locally by using VSCode's "Remote-SSH" as introduced in the blog below.
https://medium.com/@christyjacob4/using-vscode-remotely-on-an-ec2-instance-7822c4032cff