It seems for me that adding modules into C++ was a mistake. The old-style approach with includes wasn't ideal, but it was well understood and all its downsides and pitfalls were well known.

Than modules were standardized and this happened in a very strange way. Usually major features are already implemented at least in some compilers before being standardized, but with modules it wasn't the case. It was in 2020, it's now 2025 and they aren't fully implemented and tested in all major compilers and it's unclear how long one need to wait to be able to use them.

Modules are also very problematic, as the article above shows. They didn't solve many C++ problems with multiple translation units management, like compilation speed. Moreover they added new problems atop of old ones. And managing dependencies may become ever more painful, because some dependencies use old-style includes and some use modules instead (xkcd 927).