The getFilters function returns the current filters that have been applied to the object (can be a report or a page). As a result, if no filter is used, it will be empty.
The short answer to how to acquire all the choices of a filter section is that it does not exist.
In Power BI, there are two types of filters: Basic and Advanced. Basically, every column in any of the data model's tables can be used as a filter target, even if it isn't used in the visuals. And the filtered values can be any value that is compatible with the data type of the column. As a result, there are numerous, if not infinite, filter combinations.
Instead, you can learn how to create filters and apply them to the report or page. Adding slicers to the report during the report creation step is also a good option.