How to Create Reusable Blocks on a Squarespace Site?
Copying Individual Blocks (Fluid Engine)
To copy blocks from one section to another, use ⌘ + C / ⌘ + V (Mac) or Ctrl + C / Ctrl + V (Windows).
Squarespace 7.1
You can save and reuse layouts by saving page sections:
Hover over a section and click the heart icon to save it.
Add saved sections via Edit > Add Section > My Saved Sections.
Note: Saved sections are independent of the original and retain design and content but may require manual setup for features like forms.
Saved sections cannot include collection pages or footers.
More detail on Squarespace support
Squarespace 7.0
There’s no built-in feature, but third-party tools like SquareTools Extension PRO allow you to save layouts as "Content Presets."