The web part is a specialized widget to display a Microsoft Visio diagram in a modern SharePoint page. It is somewhat similar to the “Visio Web Access” web part in “classic” SharePoint.
In addition to the stock “File Viewer” web part which you could use to display Visio diagram, this one features the following:
File browser, specific to Visio diagrams
You can specify which page to show first. You can specify either page name (like “My Second Page”), This only works if the diagram has more than one page. In case the page you selected does not exist, it will default to the first page.
Select default zoom level
You can set the default zoom level for the diagram.
Full width and application page mode support
You can add the web part as an application page.
Support for custom width/height setting
You can specify the width and height of the diagram. Can be in percents (also percent of the screen) or actual measurement units (like the classic “Visio diagram view”).
Support disabling menu items
You can optionally hide diagram toolbar, diagram boundary, border
Support disabling some interactivity
You can optionally disable hyperlinks, zoom, pan, and the navigator
For more information, please check the web part site: