I also had to generate my own godot-lib AAR files. The documentation certainly doesn't make it clear how to do this, but here's what worked for me:
I followed the instructions on compiling for Android:
https://docs.godotengine.org/en/stable/development/compiling/compiling_for_android.html
Then from the godot/platform/android/java directory:
./gradlew copyDebugAARToBin
./gradlew copyReleaseAARToBin
This will copy the built AARs to the godot/bin directory. Note I'm using OSX so the command line syntax may differ on Windows.
I needed to do this to export my project for Android. Merely updating the APKs for custom builds doesn't use the updated AARs. So I had to find the built AARs and copy them to the android/build/libs directory after installing the templates in my project.
I'm no sure if this is what you need for FDroid, I hope it helps.