This was rather easy with my rooted Android phone. However, when flashing it with Android 6 due to some memory leaks, root access does not work anymore. Neither by adb, nor by Kingoroot and Kingroot.
To export Whatsapp messages, however, I urgently need the whatsapp.cryptkey. And this key is only accessible in a rooted phone.
So I went down by another strategy by using WhatsApp-Key-DB-Extractor-master script on the Mac. To make this work, the JAVA JDK needs to be updated to at least version 7. The JDK needs to be manually downloaded and installed from the Oracle site
oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
In a next step, the Android Debug Bridge needs to be updated from the terminal as the version in the zip file listed the phone as being inactive
brew cask install android-platform-tools
Then we can run
WhatsAppKeyDBExtract.sh
which puts 5 new files
axolotl.db chatsettings.db msgstore.db wa.db whatsapp.cryptkey
into the
/WhatsApp-Key-DB-Extractor-master/extracted/
folder. Move this folder back to the SD card where the “Backup Text for Whats” App can find the key to export all encrypted Whatsapp messages.