Let me provide an additional step on how to remove transactions that have been categorized in QuickBooks Online (QBO), @Swordbooks.
In QBO, we first need to undo the categorized transactions before you can exclude or delete them.
To undo the duplicate transactions, follow the steps below:
Once you Undo the transactions, they'll move back to the For review tab. Then, follow the steps provided by my colleague on how to exclude or delete them.
Check out this article for future reference to help you with your reconciliation process: Reconcile an account in QuickBooks Online.
If you have additional concern or queries about online banking transactions, let me know by replying to this thread. I'll be there to help.