Some apps do actually generate random private keys and check if they have a balance. But the creators pre-load the app with a few known addresses that do contain Bitcoin, then display these as "results" to trick you into believing the app works. You'll be asked to pay a fee to "withdraw" the found Bitcoin, and then you get nothing.
No Android APK, desktop software, or supercomputer can "find" a private key for an arbitrary Bitcoin address. Any app claiming to do so is either: download bitcoin private key finder apk better