The Template Builder's mobile layout is a fixed system and is pretty simple once you get used to it. We have two controls– "do not stack" and "hide", which allow you to change how your layout appears on desktop and mobile email clients.
Stacking Content on Mobile
When desktop is converted to mobile it will stack all of the content within your row into a column, then it will stack the next row, progressing through your email.
With the new "do not stack on mobile" control, a row can be fixed, so it displays the same on desktop and mobile.
To access the "do not stack on mobile" setting, hover and click on a "Structure" block within the template.
The "do not stack on mobile" setting will appear in the "Structure" properties menu on the right.
Hiding Content on Mobile/Desktop
At the content level, you can select individual images or other objects, and hide them on either mobile or desktop display. This allows you to substitute different image ratios for images on desktop and mobile.
Select the object in your email
Select the hide control for either Desktop or Mobile display