I'm familiar with lean methodology and aware that ideas don't really mean much, but at the same time I'd like to work on some big problem that's compelling. I know that I'll probably pivot a lot but just to start out what general problem would you reccomend I try and solve?
I am happy that you have not started off developing something without really talking to your customers. Technology by itself does not mean much. First you need to decide the domain. Do you want to solve the problems of old people, patients, school kids, moms, unemployed youth, unemployed seniors, grocery store owners, car owners, car mechanics ...figure that out. This usually should come from one of your hobbies, some thing you do regularly or an area of your passion. It could be water cycling, for all I care.
Now look at the way people are doing stuff or trying to get some things done in the chosen area. The problem happens only when someone wants to do something. Either he is not able to or it is very difficult,or it can be improved.
It becomes a big problem based on the seriousness of the tasks to be done and the number of people who are trying to do this task. Everyone in the world seem to be trying to form groups and stay connected with them easily, for free. That is why Whatsapp is a great success.
Hope this clarifies. Nothing comes out of technology in isolation. First connect with a selected group of people and see what they are struggling with. Then see if you can provide a solution , using technology.
All the very best.