Currently, it is not possible to hide all the markup in the editor natively. However, some themes make them barely visible, resulting in an even more minimal writing experience.
You can browse our Styles & Themes website and, under the Editor Themes, select Hidden Tags to see all such themes. This link forwards you right there: Hidden Tags
Some of our recommendations include:
You can even customize the entire editor to meet your needs. For that, please refer to our Editor Customization Guide.