Hi @Matias Geronimi
Perhaps you can try using a rectangular container to control how the data region is rendered in the report. The report first renders the objects in the rectangle relative to each other, and then renders and places other objects relative to the rectangle, that is, ignoring the objects in the rectangle and treating them as a whole.
For the use of rectangles, you can refer to this link: https://learn.microsoft.com/en-us/sql/reporting-services/report-design/add-a-rectangle-or-container-report-builder-and-ssrs?view=sql-server-ver16.
I did a simple test with two tablix placed in a rectangle and aligned, and cangrow set to false.
Preview in Chrome:
Best regards, Aniya