Backlog in terms of Kanban/Scrum Boards are a whole different topic.
Please be so kind and open a new thread here in Community if the question is still current.
Please also explain what is meant by "does it create a new instance" in particular.
If the question should be about import/export of Jira Cloud please be so kind and rephrase your question so the Community is able to understand and able to help better.
You restore your backup from within an existing Cloud instance. That may be your current instance or another one.
The article I linked in my previous answer above describes how to start the restore:
Restoring the backup will overwrite all data in that instance.
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