Octonauts is not explicitly vegan, but checks all other boxes and is also a bit educational.

Let me introduce you to non-vegan bananas (tldr: if you want to be sure, buy organic bananas)

Earthlings (2005) was life-changing for me, opening my eyes to veganism. A more recent version is Dominion (2018).

But these deal with a gruesome topic. Planet Earth (2006) is more suitable for “favorite”. It blew me away, because I’ve never seen wildlife footage like this before.