To be fair to Harry I do think he has a genuine love and interest in Africa. He has spent a lot of time there over the years - certainly before he married/had kids. He would need to be careful about the content of the documentary though - he can't afford to be filmed moaning about his life in Africa again.
A documentary of him helping with conservation efforts etc. and him just being 'Harry', interested in other people and not 'preaching' would do him the world of good. He has a very good rapport with ordinary people he needs to show that side of himself more - that is where his value lies.
When you think Omid Scobie is a super fan of theirs - he is really not helping them writing this book.
It seems obvious that the book will largely slag off the Royal Family. Even if Harry and Meghan have absolutely nothing to do with it- the moment it is released and serialised the whole shit fest will start again and people will attribute what Scobie says to them (or insinuate they have fed him the stories)
They are never going to be able to get away from this 'feud with the RF' and that being the only thing that people associate with them. It is all so toxic.