I would like to be able to make nice looking installers like GOG does for their game distributions. I've been looking at the installers and I realized they use Inno Setup for the installer but when I make a setup file with Inno Setup, it looks like a standard install wizard. I tried looking around for how to change this and found Graphical Installer so I tried using that but it just made it look like a generic "graphical installer" made setup program. I don't know how to make a custom and unique looking installer like GOG with Inno Setup.

As a side note I noticed that I can open GOG installers with 7zip as an archive but I can't open a normal installer compiled with Inno Setup as an archive and when I try extracting all files from the installer with Innounpacker, I can not recompile the Inno Setup script it unpacks even though it supposedly unpacks all the files that would have been there when it was first made. This leads me to believe they use an extra step or some other program in the creation of these installers and I just wanted to know how to replicate these but with my own designs of course.

Sorry for the long post I just wanted to give as much information as possible to try to get help understanding this.

InnoSetup is highly customizable, and you can also have access to the source code to do even more... it needs some work however, you won't find much "ready to go"
Tools like ISSkin or Graphical Installer are extention to it that should help with that job, but again if you want to have a fairly unique look, you have to create/supply the resources needed and script accordingly

No can do. It's the elfves, you see, they make the installers. And unless you're a union member, you really shouldn't try and do their work.

I was hoping it would be something like this :)

https://youtu.be/78gt7pfjlCU?t=40

Some time ago they used an encrypted rar format for the .bin files and the setup unrared them using the correct password (hash of the game's id from what I recall). So even though Inno Setup was used to create the executable and add any necessary registry entries, the rest of the files were just an archive.

I am completely new to Inno Setup and making installers in general and do not know how to program or work with source code. I know this is probably my biggest problem but I did not realize that this all could be done with just Inno Setup. I do not mind making graphics and layouts for it because I do things like that a lot but its the implementation with code and scripting that I do not understand since I have only ever made instalers using the wizard.