Post migration from Xero, QBO wants to match transactions in the bank feed to old cheques and Sales Receipts. How do I stop this from happening?

Let me share how QuickBooks integrates with banks when it comes to handling transactions, @doone.

When QuickBooks downloads bank data, it will automatically look for a match with any transactions you've already created manually.

For example, an existing transaction has the same amount as the ones you've downloaded or imported, QuickBooks will prompt you that this can be a match.

For now, the option to stop the auto-match feature in the bank feeds is unavailable in QBO. However, you can manually unmatch this transactions by clicking Undo under the ACTION column.

 If you want to unmatch multiple transactions, you can simply check each transaction and click the Funnel icon, then select Undo.

QuickBooks Online analyzes all the information received from the bank for each downloaded transaction. You can assign and categorize these transactions to easily review them.

If I can be of further assistance, please let me know by posting below.