Not exactly - it was in the source tarbal available for download from the releases page but not the git source tree.

I don’t have a source but I think it is safe to say given the large corporations and government institutions that rely on XZ utils. I’m sure Microsoft, Amazon, redhat ect are in talks with the federal government about this

You just run the executable

The drm-free marketing that gog does has been successful, but it is just marketing. While It’s true that games sold on gog are drm-free, every game sold on gog that I’ve looked into is also drm-free on steam. The only real benefit is that the gog installers are more convenient for backups than using a steam back up tool.

Because all changes are transactional so you can easily revert to a previous system state if you break anything

Atomic desktops make all of that way easier though