Ask HN: How to find a topic and motivation for a side project?

I'm 27, I'm a SW Engineer and I have some experience also as a Data Scientist. I know how to create webservices, android apps and I have knowledge about artificial intelligence (I have a master degree in this area).

I have the feeling that I have a wide knowledge of a lot of tools, and somehow I would like to do something that is mine, but I struggle to find the project where to apply them and the motivation to keep working on my own for a long time.

Any advice of how to find the topic and motivation? How did you start yours?