OSGI does not support multi-dimensional arrays of values, but just simple lists.
When you need to provide more complex data as OSGI parameter, you should consider to package the configuration in a different format (e.g. as JSON file in the repository, or a node structure), and use OSGI to configure the path to it.
Definitely, OSGI configurations can contain string values for a configuration. For the specific string value, you can configure a String representation of a JSON Object. When your OSGI service is obtaining the configuration, you will expect to get the String value. With the String value, you can use a common JSON library like GSON, org.json, Jackson, or any other JSON library serialise the String to a JSON Object. Then you can use the JSON Object to get values within the JSON String.
Just make sure your configured value is a valid String formatted JSON object. Maintaining these configurations can be a nightmare.
I won't recommend Complex structures of JSON or XML, String formatted, because it is be hard to maintain in OSGI configurations. It might be better to create a configuration of String (OSGI will show multi-field string configurable input fields) rather than using complex structures like JSON or XML in a String format. Example:
@AttributeDefinition(name = "MultipleValues", description = "Multi Configuration values")
// from example, https://helpx.adobe.com/experience-manager/using/osgi_config63.html