I got the point on how important to have a direct option to import templates within your QuickBooks Online (QBO) account.
The option to import our own template in QuickBooks is no longer available. However, you can check for a third-party app that helps upload your personalized form from outside QuickBooks. Integrated applications are available to download through the QuickBooks App Store.
You can also search for the app within your QBO account. Follow these steps:
On the left panel, click Apps.
Go to the Find Apps tab.
Use the search bar to look for an app.
Additionally, you'll want to make use of the built-in editor to personalise your sales forms. Let me guide you on how to do it.
Go to the Gear icon.
Under Your Company, select Custom Form Styles.
Click New Style.
Pick a sales form type. Follow the steps that'll guide you through the rest.