Yarn develop --watch-admin is not working

I am developing a local plugin and in this process I need to run
yarn build & yarn develop to even see the smallest of changes to reflect on UI.

Fortunately, recently I came to know we can use yarn develop --watch-admin command while building local plugin. But, it is not working. URL is generating only for http://localhost:1337.
I am receiving 404 for http://localhost:1337/admin