Bivariate color polygon renderer is a QGIS plugin for creating visualizations based on combination of two variables.
The plugin can be installed directly from QGIS Plugins menu.
The website with description is available here: https://jancaha.github.io/qgis-plugin-bivariate-renderer/.
The plugin page is: hhttps://plugins.qgis.org/plugins/BivariateRenderer/.
The render is located in the "Symbology" menu for polygon vector layers.
The legend in layout has its own icon on the left side, or can be found in "Add Item" menu as "Add Plot item Bivariate Renderer".