This plugin adds a Responsive line break item to the rich text toolbar. Put the caret where you want the break, tick the screen sizes it should apply to, and insert it.
Breakpoints
The screen sizes come from settings.viewport in theme.json, through the same core function that drives the editor’s @mobile and @tablet states. Themes that do not set it get the WordPress defaults.
In the editor
A small marker shows where each break is, even at widths where it does not apply. Hover it to see the screen sizes, click it to change them.
Development
The editor script in build/ is compiled from the TypeScript sources in src/, which are
included in this plugin. To rebuild them:
npm install
npm run build
The build uses @wordpress/scripts (webpack). package.json and tsconfig.json ship with the
plugin so the output can be reproduced.
Screenshots
Choosing the screen sizes for a line break.
Markers show where the breaks are. Hover one to see which screen sizes it applies to.