Themes have the ability to provide breakpoints; however, they cannot be automatically discovered if new ones are added once they have been installed. Drupal only reads breakpoints provided by themes when a theme is either installed or uninstalled.

Inside breakpoint.manager, there are two hooks: one for the theme install, and one for the theme uninstall. Each hook retrieves the breakpoint manager service and rebuilds the breakpoint definitions. Without any extra deployment steps, new breakpoints added to a theme will not be discovered unless these hooks are fired.