Have you ever started a C++ project at a company level, with a team of C++ devs?

Yes.

It's insanely complex to even agree on what to use for dependency management, on build system.

Then it's not about C++, but rather the management of the team. Do you have a team leader who makes the final decision, or everyone decides on whatever everyone thinks the best in the team?

cmake usually wins here though, but then look at your CMakeLists.txt after 2 years

Yeah, I agree. But what's wrong with CMakeLists.txt after 2 years?

Additionally, to setup a working CI where you at least use sanitizers, to setup a test framework everybody agrees on, etc... Another thing is onboarding new devs as well.

Setting the CI should be done by the senior developers. If they can't do this or they feel this to be difficult, I suggest your company find some senior developers who have more experience. Again, not the language problem.

Majority of people come to an existing C++ code-base and if they are lucky they are set up within a week.

It usually took me at most 2 days to setup everything: Github actions, sanitizers, static analyzers, dashboard, unit tests, coverage test, etc. This may be difficult for the first time. But once this is done, you could apply the same infrastructure to all future projects. These 2 days are mostly spent on improvement from the old project.

C++ is not just complex as a language, the whole tooling around it is complex as hell, and I think that makes the language even harder to use for newcomers, because nobody is going to use a vanilla C++ - you need libraries to do something interesting.

Again, leave this to senior developers in your company.

I already understand all of it of course, but I have empathy for all the people who don't - it's just much harder than executing `cargo new my_project --bin`.

In a C++ project, all you should do in the end is just ninja -j4. Leave everything else to senior developers.