Arcgis Pro has exporting option of .mapx and arcmap has .mxd.
.mapx and .mxd are not even remotely related. .mapx file extension is a file type that resides in a web server and delivers content through a web browser.
.mapx is more closely related to the idea of a shape file.
You will need a software like MapDotNet to open the .mapx and you may be able to convert it to a shape file. But I have no idea if you can.
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