The browser answer deserves more than a paragraph because with a keyboard attached the phone stops being a phone.
With a folding keyboard and a large-ish screen, the web suites are genuinely fine for a couple of hours of work. Not pleasant, but fine. And you are right that nobody suggests it, the question is always framed as which app to install, so the answer arrives as an app.
Two things that make it better and are not obvious: install the web app to the home screen so it is not competing with tabs, and turn on the desktop-site setting, because several of them serve a stripped mobile layout by default that is missing exactly the menus you need.
Where it genuinely dies is offline, as you say. On a plane or a train through a tunnel it is nothing, and that is precisely when I most want to work, so it cannot be the only answer.