How do you actually get an old 4.20 project to open on Linux?

I’ve been trying to help a friend mod Helium Rain (I won’t link here don’t want be flagged as spam) and the source code is avaliable on github.

But UE4 complains about incorrect version project, and then crashes due to missing Modules, one being “HeliumRain wtf?”

According to the friend the game works with Unreal 4.20.3, but the .uproject has “4.22” in it, when open it with either 4.20 or 4.22, it complains about the version being wrong, converting the project, and then proceeds to replace the version string inside the “uproject” with a UUID, which makes no sense to me.

Using UnrealBuildTool generates useless project files it runs, and then I run “make” and it doesn’t do anything, just finishes and has no binary generated.

Using RunUAT it’s god damned slow compling crap for IOS and android, and still doesn’t produce a Linux binary.

Why is it so hard to just build the project? What Am I meant to do to get it to compile?

Why is there not a simple process of “open” and then “compile”?