If it's too long to read then you can safely skip to "C++20 Modules" section near the end of the article.
As work, now, we mostly use C++11 and C++14, some projects are C++17, but I am not aware of a single C++20 project, I think all active projects that are C++03 or below have been migrated to something more recent.
Just a data point.
I was quite surprised to read this in their roadmap, as Unreal's codebase is quite massive and also uses some custom build tools.