Hi @nemonobody, I believe you are running into one of the ugly sides of the software development industry, but it's good that you are thinking and asking about it, rather than trying to "go with the flow" and compete with everyone else.
First, please keep in mind that doing things like working on open source code, writing a blog, presenting at conferences, etc. is work. If your employer expects you do these things and doesn't offer to compensate you for it somehow, then they are exploiting you, and you should push back. This goes for everyone in the industry. Now, does this mean that no one should blog, contribute to projects, or present at conferences if their employer doesn't pay them to do it? Of course not, if that is something that genuinely interests them and they derive pleasure from it, they should. But there shouldn't be an expectation or requirement to do it for free, certainly not from your employer. Think of it as volunteer at the SPCA, or helping cleanup a local park. You should do it for the enjoyment you get from being helpful and improving your community, not because you think your career depends on it.
Now, the second question is: are you competent? Based on my previous paragraph, remove any data points and experiences you have that don't actually relate to your job. Concretely, it doesn't matter that you don't speak at conferences, or that you don't blog, or don't have any open source projects. All that is fine. It does matter what your boss and coworkers think of your abilities and work ethic. If your manager is complimenting, that is a good sign. You're meeting your deadlines, learning and applying, those are all good signs. The only negative I can spot from your post is that you don't know all the technologies your company uses. Given how big the codebase is, and that you've been there only a few months, I would say this is perfectly reasonable. You already said you're learning actively, as long as you keep that you should know more and more of these technologies and become even more valuable to the company.
So, all that being said, what should you do? If you continue to have doubts about your competency, that is completely fine. Take concrete steps to verify them. If your manager is approachable, ask them what they think of your performance. Ask them if they think you are working as well as you could, ask them for specific areas in which they think you can improve. In my experience, most managers are happy to hear their subordinates taking initiative to get better and will do what they can to help you along.
Finally, if you really do think you want to start having side projects, or speaking at conferences, start taking small steps with that. If there is some open source library you use, see if you can close a bug, or file a better report. If you want to blog, try writing just one short article about something you learned, or some interesting code you wrote that week. Pick small, definite tasks and complete them regularly. You sound like a conscientious person, so I don't doubt that you will be able to make progress.
Good luck, and please let us know if you need more help or advice!