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.
That is canon for ya, should have used INSERT_OTHER_MANUFACTURER_HERE$ /s
But if you look how much manuals get ignored by the customer, it doesn’t make sense to put work into them.
It is much better to let a YouTuber do it, by lending them the product and throw small amount of money against them.
Manuals are just there for legal or certifications requirements these days.