Hello,
I have a category with sub-categories. These are e.g. expenses for all hobbies. I would like to get a sum of this top category over a certain period (also over all the positions ever in this category). Ideally as a "cumulated" report - where every month the sum of expenses of the month + all before is shown. But also to get even only the total would be good.

Thank You in advance for a hint how to do it?
Kind regards

I would start using an Income and Expenses by Year report. Using the Filter configuration of the report you can limit that to include only the categories you want. Using the right mouse button to (de-)select a category also (de-)selects the subordinates. On the Range tab you can select the time spans to be reported and on the Rows/Columns tab you select the detail level.

Hope that gets you started.