It can be difficult for an outsider to contribute to open source projects. Very large projects don't have simple, easy-to-fix, outstanding issues. 'Outsiders' are generally not aware of smaller projects that would welcome their contributions. And these smaller projects generally have a very niche use. For this reason the majority of open source contributions I've made have been to roguelike games, and generally those that I'm extremely familiar with.

To be honest, a PR from someone who doesn't use your software, who is unfamiliar with its structure and only wants her PR merged so that she can say 'I am an open source contributor' is a hassle.

I also think it's unfortunate that the author thinks her feelings might be due to impostor syndrome, when she is quite clearly an impostor to some degree.

My best advice would be to stop looking for a repository to contribute to. Just keep using software that you find helpful, and eventually you will find yourself using a small library with some missing features that you can add. Or, just host all of the software you write on GitHub. Create nice readmes. Create issues and releases. Talk about your project in a forum of likely users. Maybe someone will contribute to your code. Boom. Now you are part of the open source community.