Newer versions of Android are able to read native libs directly from the apk without extracting them if they are stored uncompressed in the apk. This is done to save disk space on the device, and the new default during apk creation, but Qt 5.12 does not handle this. To compress native libs again add android:extractNativeLibs="true" in AndroidManifest.xml to the application tag.

Please have a look https://github.com/denisgottardello/QtAndroidServiceExternalLib where you can find how to start and stop a service