Create a graph using a query

I created a custom query field for the person entity, where I count the total number of unfinished tasks per person. What I would like to do with query is to create a graph in page to list in descending order the number of tasks that each is user is assigned. The problem is that the option to choose the custom query is greyed out and can’t be selected. Any reasons why this is happening and any potential workarounds

The simplest solution is to use a grid instead of a graph and whilst that works I still can’t sort out the values.

Screenshot 2023-03-06 143336