"it's been done" and "the opportunity is gone" are completely different claims. Being first has almost never been how software wins. Winning comes from executing better, serving a specific underserved slice, or building for a market that others ignore or serve badly.
Interesting app dev idea: build the same app as one that already exists. But do it for free. Then add some other premium features (provide more value) and charge for over delivering.
Asking Opus 4.5 for a dollar amount that it would wager that a certain implementation will work correctly can be a fun way to see how confident it is… It just responded to me saying “Honestly? $50.” 😬