The app does not collect any of your data.
Any data that you enter yourself, such as the settings, is stored locally and never leaves your device.
The app uses the official Hacker News API service to retrieve data from the website. Being a web service, it may collect data such as your IP address and basic information about your device.
The project is open-source, so you can check out the code on GitHub.
If you've got any questions or comments, feel free to reach out to me on Mastodon!