Depends on the user & use case:

Researchers use LaTeX heavily for papers. It has a learning curve, but once mastered it is very powerful.

Markdown is being increasingly used for code documentation nowadays. `readthedocs`, github pages work well with markdown syntax

Publishers tend to layout professional documents with Adobe Illustrator / InDesign. All the common magazines generally use it, unless they have some custom sauce built-to-order

I have used Obsidian before but I found it more useful for researching instead of pure writing so now I just write any technical notes in neovim. Many folks (as myself) try to make neovim a kind off IDE for programming but I think first of all it’s a powerful tool for writing texts. I just write markdown files in (neo)vim and because of movements and mouseless interface it’s doing fast and focused

For me writing markdown using VSCode with with Neovim keybindings approaches that rich text and rich code environment.

Of course, when using markdown(/mermaid/tikz/etc.) creating diagrams is severely limited unlike point and click alternatives. I haven’t seen a good solution yet that isn’t too restrictive or slow.

https://nota.md is my absolute favorite writing tool.

It's like a markdown editor with some code editor features, like for example multi cursor/selection, auto bracket closing, option + up/down to move/reorder lines, things like that. The "hide markdown" function makes it very nice to read as well.

It works on plain markdown files, which is really convenient for many things. No subscription, just a very reasonable one time price (they used to have a free trial/beta, I don't know if that's still the case).

I use it to draft pretty much everything I write, I just copy paste to confluence/gdocs/slack/wherever.

Pandoc with a paste image plugin for markdown, in vscode with vim plugin or just vim.

Notion if you want to quickly share things. But I would recommend using something else because they don't have offline support and they don't allow downloading pdf format of nested articles without a paid tier. Also no vim bindings. But I still use it as super fast to share, easily formattable and looks nice.

https://jupyter.org does it all, code and markdown. Output can be html, pdf, or LaTeX.

https://jupyterbook.org provides the book stuff - toc, bibliography, sequential numbering for chapters, sections, equations, figures, tables, ...

If I were tasked with writing something like a book right now, I'd try very hard to get a copy of Microsoft Word 2000, and the update from 2007 that allows it to handle .docx files.

Why? The outliner mode in that was super productive. Everything since is a piece of junk.