If you spot something not quite right in flatnotes and have the skills to fix it, then I'd welcome the pull request. If the fix requires a large change, then it would be best to open an issue first to discuss.
If you're interested in adding a new feature to flatnotes, then please open an issue first to discuss the idea. This will help to ensure that the feature is a good fit for the project and that you're not wasting your time. Whilst I'm keen to improve flatnotes, I'm committed to keeping it simple and focused, which will mean saying "no" more than I say "yes".