Why Oracle 19c Database EM Express Webpage is not opening in Microsoft Edge?
I want to open the localhost:5500/em

What makes you think that the web site is being offered on port 5500?
I don't know about the Express version, but full-blown Enterprise Manager is provided by a running, Middleware process.  Is there a Window Service that you need to start (or, for whatever reason, has failed to start?)

... in the SQLPLUS command prompt I am able to login successfully ...

That's because the Database and the Web Site that you use to manage the Database are two completely separate things.