To write a blog or some page content in WordPress.com, there are two different editors. One is classic editor which is the old one and another is the new block editor. I found one thing is missing and that is good markdown support. Markdown is very much supported in everywhere on the internet like StackOverflow, GitHub. But why there is no good support in WordPress.com editor that I am not sure. You can write markdown block editor but it is lack of good support. The way they are working on their block editor and updating with new features but there is no work is happening on markdown support.
The old classic editor has good markdown support but it is old and WordPress.com is asking people to use new block editor which is not having good markdown support.
Below is some links related to markdown support from WordPress.com help.