Hello there, @aa1745,
QuickBooks Online will not calculate the VAT if there was an adjustment made from QuickBooks Desktop.
I suggest running these reports on an Accrual basis for All Dates when checking balances from QBDT. This is to ensure an accurate balance are shown and confirm the accuracy of the data migration.
- Balance Sheet
- Trial Balance
- Customer Balance Summary
- Supplier Balance Summary
- VAT Summary
You can also read through this article for your guidance with the information I shared above: Post conversion checks for getting started with QuickBooks Online.
Should you have follow-up questions, please let me know. I'm always around whenever you need help.