I find markdown is very handy and useful to write something for the internet. It is text based and easy to be placed in a source control like Git. Also it is easy to collaborate with your team member. Markdown is supported in many major places on internet like GitHub, StackOverflow, Bitbucket etc.
WordPress.com supports markdown as well but writing with markdown in WordPress.com block editor don’t have first class support. Block editor is good but not for those people who wants a text based writing experience like markdown.
One good option is Simplenote. It is a note taking app from Atomattic which supports markdown. You can draft your blog in markdown with Simplenote and when you are ready, you can copy the content and paste in WordPress.com block editor. All the formating are automatically preserved.
Read more on Simplenote here.
One negetive point which I found in Simplenote is, it don’t have a spell checker built in.