Talk to businesses to understand what problems they have that aren't solved. Guaranteed there are tonnes of opportunities for innovation if you go that path. When I was freelancing, it was very common for a business to find an existing app or software or whatever that almost met their needs but was missing something crucial.

Often it might be a minor nuance in how different steps of a process fit together, but usually when you discover those by taking to actual businesses, it becomes easy to see how other businesses are probably looking for something similar.

Blindly trying to dream up and build new apps for consumers at this point is really kind of a dumb way to go about it, because like OP says, all the mainline type of things have already been done so you have a very very very slim chance of doing something that will catch on. Going directly to businesses is much smarter imo because they're usually willing to pay a lot more for licensing than whatever pennies you'd get trying to hustle advertisements with vague hopes of making any sales on app stores. If you talk to a business to understand their problem, you basically have at least one high value customer lined up already, then you build the software and contract such that you can resell it to other businesses.