Say more about what you can't seem to find here. The idea that Word is not a serious tool, or is not suitable for anything longer than a letter, is just laughably false given how widely used it is in pursuits orders of magnitude more complex than a letter to your Aunt Millie.

I'm being a LITTLE snarky, but I also am genuinely offering to help, if you want it.

Not the parent poster, but I believe he asked how you can disable direct (ad-hoc) styles manipulation? That's something I'm also interested in - my ideal Word document would be the one in which I define styles to be used and every paragraph uses exactly one of these styles and the user can't say "I'll make these few words 14pt just because".

For example, https://www.officetooltips.com/word_2016/tips/protecting_wor...

I believe another replier has noted how one may do that.

IIRC Word used to have an "outline editing" mode where normal visual styles were largely ignored and replaced with a uniform set of rendering styles. Its principal feature was the ability to fold nested structures (chapters, sections, etc) and easily reorder them.

It still does. The macOS version has it in the menu bar: View > Outline.