If you want to avoid web frontend, then stick to mobile app development. DRF as someone else mentioned helps. I recommend front end development because they have guidelines and make thing easier to implement (iOS is much much easier). You can’t make a usable app without doing both frontend and backend.
As the last person said, do a project that helps your community. Don’t think big, or a million dollar app idea, or money in general. Think impactfulness on YOUR community only.
Backend code is not revolutionary. If you want business logic to be revolutionary, then find a computer engineering job or code a huge algorithm. Django and Flask are meant to be full-stack development packages. When you get a job, you can think backend only, sure, but you’re asking for a USABLE app; thus, my second paragraph still stands.