Currently (as of 30^th Sep 2020), the default Select Box form element supports only one dependency field to control the available options based on the "grouping" attribute.

Here is a new plugin called the "Multi Dependency Select Box", which belongs to the Form Field Element plugin type.

This plugin is highly similar to the default bundled Select Box form element, but with the additional capability to configure multiple dependency fields to control options.
Configuring the multiple dependency fields for this plugin is also highly similar to the default Select Box.

To control options from multiple dependency fields, do add multiple grouping values for a single option, with comma as the separator. (Example grouping value --> A,2,Blue)

Do try out the plugin via the resources you can download below!