I set up a small charity's site I maintain to use GitHub pages and Jekyll. The in-browser editor for markdown is good enough for the non-technical users, and GitHub pages takes care of rebuilding the site. The revision history is handy in case someone does something weird and we need to undo it.
I believe that GitLab pages offers something similar that also supports Hugo, but I opted to use GitHub+Jekyll as I personally find it significantly easier to custom-build a website than with Hugo (I really struggled with on some basic stuff, e.g. I had a lot of blank pages at dir roots (e.g. /something/goes/here would have blank pages at something/ and something/goes/ etc)). Hugo feels over-complicated to me.
Tina CMS [1] is something I bumped into (haven't tried since I'm not enamored by React, or rather, JavaScript based sites for blogs). It provides an editor right on your site, and works with static site generators like Gatsby and NextJS.
Not really in a separate access-restricted area of the site, but I use https://forestry.io/ to update my (netlify-hosted, github-backed) blog when I don't have access to my own machine (or correct a typo from my phone).
Netlify CMS has been impressive for me set and customize.
I just wish these static sites has a smooth way to do image layouts (crop, resize, layout and picset generation). I'd give up MD for that, html+emmet is basically just as simple as markdown.
* edit as for access, I gitlab pages host the static site and leave gitlab to handle the netlify cms auth part.
I believe that GitLab pages offers something similar that also supports Hugo, but I opted to use GitHub+Jekyll as I personally find it significantly easier to custom-build a website than with Hugo (I really struggled with on some basic stuff, e.g. I had a lot of blank pages at dir roots (e.g. /something/goes/here would have blank pages at something/ and something/goes/ etc)). Hugo feels over-complicated to me.