Can i generate e-invoice in the prescribed format and upload it to the GST portal designed to authenticate such invoices?

Glad to have you here in the Community, @office211.

QuickBooks only allows you to customise invoice for GST to process e-invoice. However, uploading it to the GST portal via QuickBook is currently unavailable. You can consider uploading it manually to the GST portal.

Here's how to customise your invoice to make it GST compliant:

1. Click the Gear icon, then select Custom Form Styles.
2. Find the invoice template and click Edit.
3. Go to the Content tab, then choose the first section (Header) of the custom form.
4. Put a checkmark in the Customer GSTIN checkbox.
5. Then, on the same window, select the second section (Table) of the custom form.
6. Select the Item Code checkbox.
7. Click Done.

I'm adding this article for more guidance: Customise invoice for GST.

You might also want to check out this article to learn more about QuickBooks for GST: 

• How GST impacts QuickBooks users.
• What is a GST-ready invoice?

Please know you can continue to reach me here with any additional questions. Thanks for coming to the Community, wishing you continued success.