There's nothing built-in to the Fusion API to support this. What you're talking about is inter-process communication, which you can read about more here: https://en.wikipedia.org/wiki/Inter-process_communication.
That article lists many different methods, but what's feasible depends on the specific situation. The simplest one mentioned is the use of a file. The add-in could periodically, check a location for a specific file and if the file exists, it reads data from it and performs some action. The Excel macro could write this file.
I've also heard of other people doing some things with sockets. Neither of these has anything to do with the Fusion API but are features of the programming language and OS.
If you're add-in is watching for something in the background, you probably want to read this article from the API User Manual. https://help.autodesk.com/view/fusion360/ENU/?guid=GUID-F9FD4A6D-C59F-4176-9003-CE04F7558CCC
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Brian EkinsInventor and Fusion 360 API Expert
Website/Blog:
https://EkinsSolutions.com