When doing npx frontity build you get a build folder in the root of your project.
Inside that build folder there is a .html file generated at analyze/module-development.html. This file is a visual report in the form of a tree generated by Webpack Bundle Analyzer.
This report shows you the modules included on each bundle and the size of each one, so that you can analyze them and maybe decide using other modules (or not including a specific module at all) to reduce the size of the final bundle.