I followed these steps:
In top menu bar, click on Build > Clean Project.
In top menu bar, click on Project > Build Bundle(s)/APK(s) > Build Bundle(s).
The Event Log pane will give the time and status of your build:
08:19 Build Bundle(s)
App bundle(s) generated successfully for 1 module:
Module 'app': locate or analyze the app bundle.
You can click on "locate" to show the .aab file in the Finder window, in platforms/android/app/build/outputs/bundle/debug/app-debug.aab
After this I followed:
In top menu bar, Build > Generate Signed Bundle / APK...
You'll get the options to sign an Android App Bundle (top option) or an APK. The Android App Bundle is selected by default. Click on Next.
The Generate Signed Bundle or APK window has several fields to fill out. "app" should be in the Module field.
I filled out the fields.
When all is said and done, Event Log did not display anything regarding the signed bundle. There is no change in the .aab file (I checked the date/time). I kept the export encrypted kit location as Desktop, but there is no .pepk file there.
Event Log does not display any errors or warnings.
(I wrote a complete article on my process here: https://iphonedevlog.wordpress.com/2019/09/17/making-an-android-app-bundle-aab-file-from-a-cordova-project/)