How would you search for a small niche?

I'm thinking of building a few MVPs for small niches that big companies don't care about, and see what sticks. I wanna do something that would be a good side project and portfolio builder. How would you go about finding a small niche with a unique, big pain point? I have a ton of big ideas, but now I'm looking for small ideas if that makes sense. I don't want to be the next OpenAI, more like my own venture builder for lifestyle projects.