About Linux VM GUI mode issue

This is the kind of thing where it's good to have "real world" experience of it first. By that I mean having e.g. two laptops (at least one running Linux) and you can get one of them to display the screen from the other. This way you can see what's happening (or not happening - e.g. you can see what is on one screen and so you know what is meant to be on the other), and after this it's easier to take what you've learned and apply it to AWS.

If you can't do that then don't worry, there's an AWS knowledge document which goes through all the steps here https://repost.aws/knowledge-center/ec2-linux-2-install-gui

The associated video walking you through the steps is here https://www.youtube.com/watch?v=tuz4RK-E6OI

There's an Ubuntu doc about it here https://discourse.ubuntu.com/t/running-ubuntu-desktop-on-an-aws-ec2-instance/13953

One difference between these is that the AWS doc is using port forwarding to make the connection to VNC through an SSH tunnel, whereas the Ubunu doc is using plain, unencrypted VNC traffic on port 5901. The Ubuntu method might actually be simpler if you're learning from scratch, and you can always add the SSH tunnel later.

The AWS doc describes how to setup an SSH tunnel using Linux, but not if your source is a Windows PC running PuTTY. If you need to do this the instructions are here https://helpdeskgeek.com/how-to/tunnel-vnc-over-ssh/