The trick about documentation is depth, not prose. You need context and understanding to write documentation "like in the old days". No amount of LLM trickery will free you from that. Once you have that source material, it's easy to re-shape it into an 80's/90's/00's doc format.

Negative example: I was looking into the German manual of my Canon EOS R5 II, and it is just fluff. Hundreds of pages, full of white space, telling me about features without actually explaining what they mean. Awful automatic translations. Their manuals used to be good (looking at my EOS 6D). But these days: oh boy.