How do I switch off customer direct debit for individual invoices (used to be able to whilst creating an invoice) in new QB environment?

You can switch off direct debit for individual invoices in the new QuickBooks Online interface by going to the invoice settings.

Go to All apps > Sales & Get paid > Invoices. Open the invoice you want to update by clicking Edit and select the Manage icon (top right of the invoice form). From there, choose Payment options and toggle off Direct Debit for that specific invoice.

Let us know if you have further concerns.