Is this installed, or portable?

If it's not installed you're not going to have a desktop or start menu item unless you create them.  I have never used the Atom text editor, or seen it under Windows, so I suspect it's third party.

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Brian - Windows 10 Home, 64-Bit, Version 1903, Build 18362

A learning experience is one of those things that say, "You know that thing you just did?  Don't do that."

           ~ Douglas Adams (1952-2001)