I think this error is because the current version in the appstore is set for mx6 – 7. One way to get around this is to change the version number of the widget while you wait for a new release in the appstore.
I’m not sure if any of the code in the widget is deprecated but to solve the error that you are currently facing you can do the following:
use 7zip or winRar to open the widget package archive. The widget file can be found by opening your project in file explorer > widgets folder.
Right click the package.xml file > edit. Change the version from 1.2.0 to 1.3.0.
Save and then go back to the modeler and press F4. Then the error should go away and you can run your project to test the widget.
Hope this helps!