Hello there, sheinz.
That makes total sense. It would be convenient to input the same class without adding it to each line separately. Let's send your feedback to our product developers. Our team will review your suggestion and might include this in the product updates.
We can follow the steps below and share with them the benefits of this option.
- Open the QuickBooks Desktop program and select the Help menu.
- Click on Send Feedback Online and choose Product Suggestion.

- Fill out the details needed and select Send Feedback.

For additional information and tips, feel free to check these articles:
If you have questions about classes and entering transactions in QuickBooks Desktop, please know that I'm here to help. Take care and have a good one!