Add additional root placeholders in a Sitecore-first JSS sample app
How to add multiple root placeholders when developing Sitecore-first
By default, JSS applications define only one root placeholder in the
Layout component, but you can add multiple root placeholders if your use case requires it.
To define multiple root placeholders:
Add additional placeholder instances in your JSS
Layoutcomponent, and give each placeholder a unique name.
Add the new root placeholders to the layout definition item in Sitecore.