Let's try to break down the several sub questions in your question:
Apache, well... is Apache. Inertia pushes me to it. But the other servers are very interesting, since they seems to be more high-performing. Anyway I have not found a good benchmark test.
The reason you have not found a good benchmark test is that there isn't one. And there isn't one because performance depends on project specifics. We can't possibly tell you which of the four servers would be more suitable for your project performance wise, if we don't know quite a few technical details about your project.
Each of the three servers (I haven't worked with Cherokee) outperforms the others in certain tasks. What are the tasks you are interested in?
The other servers use their own modules, but is there some significant module available for Apache and not for the other servers?
Define significant. What's significant for your project will probably not be for mine, and vice versa.
Is this a big problem in a production server?
Depends on the project, and your skills. Also, define "big problem".
I would see if the vulnerabilities were patched quickly, but where I can find these data?
Check each server's issue tracker. I'm afraid you'll have to do your own research on this one. Also, whatever's true today won't necessarily be true six months from now. Open source communities aren't exactly stable in that regard.
Furthermore, how much is simple to switch to / from Apache? I mean, if I now decide to install Apache for inertia but in a future I want to try another server, how much is simple to do? On the contrary, if I decide to try one of the other servers, how much is difficult to come back to Apache?
Depends on your project, on how exactly you utilize your web server, and on your skills.
What are the main differences between Apache and the other servers (httpd.conf, .htaccess, modules), and how much they are simple to learn?
Again, you'll have to do your own research. Start by checking each server's documentation. "how simple" is unanswerable, depends on your skills and your definition of simple.
Are there some other aspects I'm missing?
Yes, there probably are. However, you've already asked quite a few questions in one, even if your sub-questions didn't have other problems, the overall question is already an extremely broad one. One question per question would be both easier to answer and a tad more constructive.
I'm afraid the only answer to your question is "depends", and that's not really what Stack Overflow is for. We prefer questions that can be answered, preferably definitely, and not just discussed.
The only way I can think of improving the question is replacing all of it with a thorough technical overview of your project. We can't comment on which web server would be more suitable for you until we have a very good idea of what your project. That said, since your project seems to be a fairly small one, chances are that there's no objective reason to pick one web server over the other. If that's the case, just pick Apache (the more popular one) and be done with it.