I suggest Archbee for writing documents. You have both internal and external sharing capabilities. Check it out and tell me what you think!

The Notion Platform is not a writing application but a database management system, which has writing functions. I love to write on the Medium platform (https://medium.com/); their UX and UI are simple and sophisticated.

The best writing apps are very many in fact, let's say ZenWriter, you can use that too. But for me it is better to use office applications of different kinds.