There is only one file type that uses the .VSDX extension:
A VSDX file is a drawing created by Microsoft Visio, an application for creating drawings and technical illustrations. It stores shapes, lines, text, and other objects arranged together on a free-form canvas. VSDX files are typically used for saving flowcharts, process diagrams, organizational charts, and other types of drawings.
You can open, edit, save, and convert VSDX files with Microsoft Visio (Windows). You can also open VSDX files with Draw, which is included in the free LibreOffice suite (multiplatform), CS Odessa ConceptDraw PRO (multiplatform), Nektony VSD Viewer (iOS), and the Google Chrome web browser (with the Free Visio Viewer extension installed).
If you do not have a program that supports the VSDX format you can still view the contents of a VSDX file by renaming the .vsdx extension to .zip and unzipping the file with Microsoft Windows Explorer (bundled with Windows) or Apple Archive Utility (bundled with macOS). Keep in mind that viewing the contents of a VSDX file using this method is not the same as viewing a VSDX file with an application that supports the format.
Updated: May 27, 2021