No one can answer this question for you. Here's a way to answer it yourself.

Inventory your domain knowledge, that is list those subjects, however seemingly irrelevant, that you know very well. Turn them upside down, forward and backward, inside out... while looking for the faintest hint of an idea, then seize on it and push it as far as you can. Don't rely on your skill to make it with a side project. Programming skill is common. It's what you know that's different from everyone else that will make it for you.

The best advice on this sort of thing is always to scratch your own itch. Solving a problem you (and others) have will give you context and drive that solving a problem you dont have wont.

This doesn't mean you have to write your own code from scratch - that's up to you. You can pick an itch that you want to create a standalone solution for, or pick an itch where you add the solution to something existing, depending on the issue and any existing related options.

A google earth web concurrent... I started to build very first basic feature: https://www.openearthview.net If you want to restart it from 0 or start from what I did, you're welcome ! I can help on defining the need/expectations. My email: clement at igonet dot fr