The tool bundles the APK with a "micro-emulator" or a runtime engine (like BlueStacks or Windows Subsystem for Android).
Many online "converters" are unreliable and may contain malware or be used to steal data. Effective Alternatives to Run APKs on PC Apk To Exe Converter Tool
There are several scenarios where an Apk To Exe Converter Tool is useful: The tool bundles the APK with a "micro-emulator"