I need to generate an unsigned, release APK (where someone else will then sign it and release it to the store- with the someone else handling the keys and e
Actually you can build an unsigned .APK just by building it:
To generate it, on the left side of the Android Studio, there is a Build Variants menu (maybe written vertically). Click it.
The Build Variants window tab has appeared, click debug and change it by release.
Rebuild your project application > Build > Rebuild Project.
Then click Run, a new window has appeared, click Run > Continue anyway > Choose the device you want to run with > OK.
The application won't work on your device but the release build version, of your .apk, will be generated into the same directory as your debug ones:
You can note that the name is app-release-unsigned.apk and it was exactly what we wanted to have.
More information on this tutorial website.