The share buttons widget has not been updated for long time. So most likely it won’t support the latest Mendix versions. At the moment, I guess you will need to implement your own solution. Each platform like facebook, linkedin has API’s and documentation on how to use the share functionality. So with combination of JavaScript snippet in Mendix and REST Calls, you can implement this. Or maybe just set on click of share button to a microflow and in that microflow implement REST call to that particular platform. Google around and you will easily find some solution. Just integrate it with Mendix.