You can use WordPress as a REST API, which allows you to read/write data from WP in JSON format.

However, this won't be as performant as other database solutions, so you may want to consider alternatives unless there's a strong business reason to use WordPress.

I've built apps without WordPress, and also with WordPress as a back-end to meet a client's requirements, so I'd be happy to discuss the pros and cons with you if you'd like a second opinion.

Good luck!