Modern, Crazy Fast, Ridiculously Easy and Amazingly Powerful Flat-File CMS powered by PHP, Markdown, Twig, and Symfony
Drupal definitely is the 800lb gorilla in the PHP space. You can do everything with it, but you'll often need to spend some (read: lots of) time getting it going.
For lighter sites, I recommend GravCMS , which does a fair amount of what you're looking for. Their documentation  is decent, as well.
How many users does your client have? It's been a while since I last played in the WP land, but is it possible to setup new roles that are more restricted?
WonderCMS – smallest flat file CMS
1 project | news.ycombinator.com | 22 May 2022
"Why I’m no longer using Obsidian Publish" by Nicola Fisher
1 project | reddit.com/r/ObsidianMD | 25 Apr 2022
Grav – A Modern Flat-File CMS
1 project | news.ycombinator.com | 21 Apr 2022
I'm going to build a CMS. What would you like to see?
6 projects | reddit.com/r/PHP | 23 Feb 2022
How to convert a single-page Svelte website to WordPress?
1 project | reddit.com/r/sveltejs | 2 Jan 2022