The main difference between a signed APK and an unsigned APK lies in the process of digital signing, which adds a layer of security and authenticity to the application.
A signed APK has been digitally signed with a certificate by the developer. This signature verifies the authenticity of the APK and ensures that it has not been tampered with or altered since it was signed. Signed APKs can be installed on Android devices without any issues, and they can also be distributed through official app stores like the Google Play Store.