powerpoint preview in VSCode

AFAIK you can't open those files directly in VSCode, however you can open them in another application by using an extension such as Open in External App (you can find the extension via the extension search in vscode).

Once installed you can update your settings.json configuration :

{ 
 // [...]
"openInExternalApp.openMapper": [
        {
            // represent file extension name
            "extensionName": "pptx",
            // the external applications to open the file which extension name is html
            "apps": [
                // openCommand can be shell command or the complete executable application path
                // title will be shown in the drop list if there are several apps
                {
                    "title": "powerpoint",
                    // This will vary depending on your OS, you can also use a PPT viewer of your chosing
                    // On Windows, could be Program Files (x86) and a different version of Office, but you get the idea
                    "openCommand": "C:\\Program Files\\Microsoft Office\\root\\Office16\\powerpnt.exe"
                },
            ]
        }
    ]
}