Related question: Does anyone know how to decrypt the Whatsapp database on Android without root?I'd like to do the same process described in the article but I'm using Android
Whatsapp has disallowed backups this way for some time.
I've seen some people advocate replacing the installed version with an older one which does allow backups (by uninstall and reinstall, hoping the uninstall can be done in such a way as to not delete the app data) then use ADB backup on that one and reupgrade before launching it, but honestly it's easier to backup, restore on a rooted phone, extract the key, then restore again on the unrooted phone to get service back (the key doesn't change afaik).
You can do this on a different phone without messing about with SIM swapping etc, you just need access to receive SMS messages on the number the backup is tied to.