Be bold and make changes. Document what you find out, what is outdated, what is missing.
Take ownership. If there's nobody that oversees overall structure, be the one to do so - at least where you're touching it or are being bothered by it.
Diatraxis gives some great insight and considerations input into writing and structuring documentation. Namely how different target audiences and doc use cases require different forms and detail levels of guidance.
My company's internal doc/guidance also links to https://www.writethedocs.org/guide/ which seems like a good source.