Linux

I recommend Obsidian with community plugins. Application itself isn't open-source but your content stored as markdown files.

God he says no Vim and everybody goes on about vim. Please learn to read. It obviously isn't for programming.

Any text editor that lets you write Markdown (all of them, since markdown can be written as a plain text file). It's simple but featureful. I would recommend Marktext.

There is still an older version of Scrivener available for free, from when they were beta testing it on Linux. It still worked well last time I checked. The Windows version also runs really well in WIne, although it takes a bit of setting up initially.

Onlyoffice

Is UI mimics ms office and has comparability with word files.

Not open-source and has some limitations without paying but works on windows and Linux. Can even be self hosted yourself to provide a web UI for access to your own files Google docs style.

Typst

You can use their online web-editor (similar to OverLeaf for LaTeX) or download the open-source engine and run it locally (there are extensions available for many text editors).

Compared to LaTeX I find it much more comfortable to work with. It comes with sane, modern defaults and doesn't need any plugins just to generate a (localized) bibliography or include links.

Since Typst is very young compared to LaTeX I'm sure that there are numerous docs / workflows that can't be reproduced at the moment but if you don't need some special feature I'd recommend giving it a shot.

If markdown fulfills your formatting needs, then there's no beating it in terms of focus and simplicity. Use whatever text editor you like. My recommendation would be Kate. It supports previewing the rendered document in side by side view.

I'd use OverLeaf. Open source LaTeX editor with cloud storage, simple setup, plugins, extensive documentation.

Neovim

If you base your opinion of vim from memes you are missing out. Anyone who can't take 10 minutes to type vimtutor in their terminal is not someone to base an opinion on. These memes come mostly from impatient people that can't read the docs. It's a fantastic text editor.

That being said, it's not meant to be used for written words it's meant to write code and config files. You want to look for a word processor.

Abiword, etherpad, focuswciter are probably the next 3 biggest on Linux behind libre and open office.

Personally I prefer markdown for most things these days but it's not exactly meant for word processing either.

Not vim necessarily, but I would really suggest thinking about a plain text editor of your choice and some of those lightweight markup languages (Markdown itself, reStructuredText, ASCIIDoc … I prefer rST, but they are mostly the same). Exactly because it allows me to concentrate on the content and ignore formatting. Besides, formatting, do you write for print or as everybody else these days for HTML? Why do you need a large word processor which is build primarily for preparing documents for print? Every serious text editor has some kind of plugins with spellcheckers, grammar checkers, dictionaries, etc.

FocusWriter for a minimalist, focused writing experience. You can edit the existing template for a dark theme and white text. I rather like the typewriter font, Liberation Mono (it was Courier something back on Windows). Give it a try. I've been using it for around 3-4 years.

Vi 😹

While I'm a big fan of Vim, it's definitely not for everyone.

I spend about half of my writing time in VSCodium, which is a community-based release of Microsoft's open source VS Code editor. There are several markdown, grammar, and focus-oriented plugins for the platform, and you can pretty much shape it into whatever kind of editor you want.

I use VSCodium for the vast majority of my personal notes, technical writing, and project documentation (nearly all of which are written in markdown format).

I'd recommend https://typst.app/. Super easy to structure text like LaTeX and 100 times easier to use :)

Norka, Apostrophe, Obsidian

If you don't need all the features of a full office suit then check out markdown and and editor like ghostwriter

I use LaTeX, and edit using Emacs. The nice thing about LaTeX is the editor you use doesn't matter.

KDE comes with its own office suite. I've always preferred libre office so I don't have much experience with it, but it's there.

What do you want from your writing software other than basic text editing?

Mouse or keyboard navigation preferred?

I've found that for me markdown is the very simplest, yet versatile way of typing out stuff quickly and regularly. And it's not bound to any one software or platform, so I use Markor on my phone and Geany on my laptop.

It depends on what you want to achieve.

Vi and it’s descendants are brilliant editors for a programmer but not for writing prose. So stay away from them. ;-)

Do you want just to write text without being distracted by an overwhelming gui or are you fine with the hint at options?

Do you want to write in a terminal?

How much do you want to format while typing? By typing the format commands into the text or by clicking on buttons or ctrl-key magic?

Do you need version control?

For each of your combination of answers there are different solutions.

If you are looking for microsoft compatibility check OnlyOffice, its amazing

Norka looks interesting. Also, Apostrophe, Obsidian

Kile( by KDE ) if you know latex.

Others are recommending Obsidian (which I have no experience with, it may be the right way to go).

Myself, I chose Logseq on a whim a year or two ago and haven't looked back. In the backend you get a nicely composed set of plain-ol' markdown files that you can cp/edit/merge as needed.

I know you said don't suggest Vim, but I use Neovim for my writing and write in markdown. Any markdown editor will do. Marker is fine. It's really easy to convert to another format like HTML or EPUB with pandoc. Markdown has minimal formatting, too, so it shouldn't bug you so much.

FocusWriter is another good suggestion if that's more what you're interested in.