Earlier quoted context omitted.
There is no "official" way for you to download it. IIRC it is stored in your Google Drive under an API key that is dedicated to whatsapp (in some kind of per-app storage). I don't really know much about Google Drive API. However, I am fairly sure that the key is in the binary on your phone, so it shouldn't be much of a challenge to get access. I think there was something like this on Github once, that no longer works…
I tried it, but I can't seem to get it to work. Possibly because I don't know the "device ID" of my Android phone since I lost it. I got an iPhone SE and turns out I can't really import the Android backup on an iPhone, and there's no way to access it either. Some backup. Damnit why is everything related to mobile so needlessly fecking difficult. I just want to read some damn plain text files that are right there but…
The main problem here is that like everything FB related, you are the product, not the customer At least, I haven't found any reasonable explanation about why Google and Apple get an unencrypted copy of your chat history but you can't. (And not for lack of trying - there are always ridiculous answers on Reddit and HN about "but if you could read your messages, so can the bad guys")