Use a terms aggregation. Not the significant_text.
Then read carefully the documentation at:
Specifically:
If you want to retrieve all terms or all combinations of terms in a nested
termsaggregation you should use the Composite aggregation which allows to paginate over all possible terms rather than setting a size greater than the cardinality of the field in thetermsaggregation. Thetermsaggregation is meant to return thetopterms and does not allow pagination.