Pico CMS
Pico CMS is a Content Management System that doesn't use a database: it renders Markdown-formatted files and generates a beautiful tree of pages based on whatever you throw in that content folder. There's no big heavy backend -- it just renders.
As long as you know basic Markdown, you'll have all the editing tools you need. Did I mention you can embed HTML code if you need to?
Because you can just do that. Yeah, I'm kinda annoyed at the flexibility Gutenberg editor takes away, why do you ask?
This is the default theme, but you can just straight-up write your own without wrestling with some obtuse PHP framework. Everything is a Twig template, so just go for it!