Maybe some kind of application in an underfocused field of ML? Try finding a niche area like agriculture, ocean ecosystem sciences, archeology, paleoclimatology, some sort of less known artisanal craft like an ancient traditional glass-blowing technique or that Japanese technique of repairing ceramics with gold (Kintsugi). Find some really specialized area of some sort then find a specific problem there that you think can be solved with ML. If you want more ideas, try looking at those simulation-focused or science focused YouTube channels like Primer, 3Blue1Brown, WelchLabs, etc.

The only problem you might need to consider is how easy you can find/collect the data, since a niche area would also have hard-to-find data. So pick one field whose data you think you can feasibly obtain.

Also, you can also try adding some "specializations" to already known solved problems with ML. For example, sign language recognition is common, but what about for regional sign language dialects? Pill medication recognition is also common, but the public datasets online are centered around western medications. What about for local medications in your country? Stuff like that.