My preferred method of finding something to build (assuming I don’t already have an idea I’m passionate about) is to pair up with someone who has deep industry knowledge in a non-tech industry (or any industry I’m not well versed in). Take their knowledge with your skill set to create a tool/platform/whatever for the given industry.

I find that vast majority of people, even top people in another field, don’t have a good grasp of what is possible with technology. I don’t say that to make them sound dumb, just they don’t know what they don’t know. You get to be the one who can suggest technologies they can use, either existing things you can glue together and/or custom code to help accomplish a task.