Can we use the QuickBooks Sandbox for testing the migration from QuickBooks Desktop? If yes, how? If no, why?

Let me direct you to the right support so you'll be guided on how Sandbox works in Desktop, Kalpesh16.

Currently, the ability to use QuickBooks Sandbox for testing the migration from QuickBooks Desktop is unavailable. You'll want to reach out to our developers team. They're more knowledgeable in terms of technical aspects and more familiar with performing tasks such as designing, building, integrating, and testing product backlog items in a more functional way.  To do so, follow the steps below:
 

1. Go to the Intuit Developer Support website.
2. Choose your QuickBooks Product.
3. Select the Ask a Question option.
4. When prompted to sign in, log in to your Intuit account.
5. Enter a short description of your concern and click Ask.

Furthermore, learn how you can keep track of your books accurately using financial reports. To know more, check out this article for more details: Track Your Cash Flow in QuickBooks Desktop.

You can always let us know if you have any questions about anything on migration from QuickBooks. We're always here to help you all the time.