Hi @eliasexner,
The way I could do it, although it is slow, is to schedule a list of API wordflows on one of the grouping attributes using the :unique elements action. Then, inside the API worflow, I can call again another API workflow on a list using a secondary grouping attribute, and so on, until you reach the last grouping and then I create a new thing with the required calculation.
I recently requested again this feature on the original bubble post and @eve was very kind to comment on my request. However, this does not seem to be something they are going to be implementing, although it would be super useful.