Let me sort things out for you, @mindy14.
First off, voiding or deleting an invoice will affect the Profit and Loss report. This is because it will remove or reduce the records of your income.However, you can create a bad debt to close the invoice but it will still have an impact on the report's expense balance section.
For your second question, the same thing will happen if you do void or delete a partially invoice.
Also, if you'd like to pull up desired formats for your invoices, you can always customize it in QuickBooks Online. For the details on how to do the trick, please refer to this article: How to customize invoices in QBO?.
Please let me know if I can be of any help with managing your invoices in QBO. I'd be glad to assist you further. Take care always, @mindy14.