You need to get a license to get the source. When you pay for the license, you also agree that you won't share that source.

ID's engines are always called "The world's most expensive xcopy". You always get the source, but you never share it.

Same model. Get the license, get the source.

See the relevant page at: https://dev.epicgames.com/documentation/en-us/unreal-engine/...

From that page:

> This page provides detailed instructions for subscribers to download the source code for Unreal Engine (UE) from the Unreal Engine GitHub repository, and to get started working with the code.

(Emphasis mine)

The UE4/UE5 source code is only available under license, but the bar to acquire said license couldn't possibly be lower. You just connect a GitHub account, click through a EULA, and automatically get access to almost* the entire source code for free.

* The NDA'ed console bits are hidden of course but all the PC code is there. Not just release snapshots either, you can see all of Epics commits in real time.

But it’s source available, and it’s not free software, correct?

It’s just free as in beer.

“Click through EULA” is the mammoth in the room.

Yes it's source available, not true free software. Kvirani never said it's free software though.

Something as abstract as "techniques" is in general not copyrightable. Worst case, there is a software patent but that is not something that is granted automatically.