From within Xojo you can run Valentina reports, even passing arguments, but you can’t modify them. I know, I already asked them the question.
I must add that modifying reports is not an easy task for users. But if that’s what you wish, in this post Report tools recommendation - Getting Started - Xojo Programming Forum one talk about NCReport Qt Report Generator Library & Report Designer (ncreportsoftware.com) and explains how it is liked to Xojo.
There is Bkeeney Shorts 2.0, see varcess that has a report designer.