Playlist layouts support custom definitions that let you make very elaborate configurations. This feature is typically only recommended for advanced users only, you need to understand your CSS to do this and test it carefully. TelemetryTV can't help debugging CSS grids for you.
Within the Layout text entry area you'll need to enter a CSS grid-area property and ensure you have a named section called "main". Beyond that you can define the other parameters of the CSS grid-area.
To do this you'll need to define a custom CSS Grid definition. See documentation available for CSS Grids.