Can a single line be added for each items so that the whole estimation or invoice do not look for verbal/writing diarrhoea?

Good to see you here, @hello-knotnknob-. 

In QuickBooks Online, you can add more lines by clicking the Add lines button below the Service Date to enter several products or services in one invoice. 

Here's how:

1. Log in to your QBO account.
2. Select the Sales menu.
3. Choose the Invoices tab.
4. Locate and click the invoice or create a new one.
5. On the invoice page, select the Add lines button.
   
   

If you mean another thing, please let me know. This way, I can provide other steps to answer your concern.

Additionally, I've attached several articles you may utilize to manage your products and services and to receive payments:

• Add inventory products in QuickBooks Online. It helps you learn about adding your goods so you can keep track of your available stocks. 
• Record invoice payments in QuickBooks Online. It also includes steps about recording partial payments in case you'll get paid only part of what is owed. 

Get back to me any time if you have additional questions about managing your invoices in QuickBooks. I'll be around to help you. Stay safe!