My company uses Asciidoc for documentation - for almost 20 years now - and it's really good. Now with Antora you can make searchable docs, and with Asciidoctor you can create most diagrams right within the text. We target HTML/PDF/Epub and it works really well.
So you get a result that is Word-quality, but separates presentation and content, and is easy to keep under version control.
Basically for anything/everything but README.md because we use Gogs and that's just MD. OK, I admit we sometimes use Word to craft a specific page, or a print-once sign.
So you get a result that is Word-quality, but separates presentation and content, and is easy to keep under version control.