Reddit and Tumblr:- solved the problem of sharing links within communities pseudonymously
Tinder:- scaled hookups
Substack:- enabled writers to monetize their periodical content
Twitter:- enabled people to broadcast extremely concise messages globally
Letterboxed:- enabled people to share their film prefs (not sure if this is a real problem, and I actually had to Google this one)
Start by going around and asking businesses near you what the biggest issues are that they face. Sometimes a solved problem in the US may not be a solved problem in another place. Or sometimes a new business trend will open up doors to disrupt traditional businesses. But it all roots back to the problem - if you're not solving a real problem, you're not going to be successful getting even 1 user/customer.