A CMS makes the backend inaccessible. Want to add inline styles to a page? You can't. Want to embed a script for some quick interactivity? You can't. Of course you could attempt to locate the theme files and edit them, and edit the configuration files to enqueue scripts but at that point you're no longer having fun.
The only thing you can do is write paragraphs in templated portions of the page. And that's who a CMS is for: people who are doing a job, and have no curiosity about looking under the hood and messing around.
That's not my experience working for CMS like TYPO3 for many years. Although actually using that power without proper training for the editors often results in chaos.
The only thing you can do is write paragraphs in templated portions of the page. And that's who a CMS is for: people who are doing a job, and have no curiosity about looking under the hood and messing around.