QB Issue Resolution:

there is only one template in QBO for invoices, no other templates can be used nor are there any customization of PO’s, sales receipts, etc

gear>settings>form delivery>customize
or in the New New QBO bring up an invoice and click customize

Resolution for Issue 'Is there an editor to create an invoice template?' available: Yes (Solved).
Source: Intuit Community forum.

Is there an editor to create an invoice template?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Invoice
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Error Recovery for Invoice [Canada]
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