Just like any .yx file (.docx, .pptx, .vsdx) in the Microsoft Office suite, the .vsdx is actually a compressed folder. That means if you rename it to a ".zip" file, you can unpack it and find its contents. In there you'll find xml files for each page in your Visio and in those xml nodes, you can find all of shape data and their values.

From there, you can process or convert this to whatever you had in mind.