I know a way to offset the prior paid invoices of 2020 in QuickBooks Online (QBO), Rose81.

Yes, you are right. Once you apply for the payment and select it back in 2020, your Account Payable figures in the Balance Sheet will be changed and this affect your current report. To avoid this, we can record journal entries in QBO. This is the last resort for entering transactions. It will let you move money between accounts and force your books to balance in specific ways.

We can use this method only if you understand accounting. You can also find an Accountant if you need one. They'll help you on what account you need to use to balance your books. Here's how: 

1. Click the + New Plus icon. 
2. Select Journal entry.
3. On the first line, choose an account from the Account field. Depending on if you need to debit or credit the account, enter the amount in the correct column.
4. On the next line, select the other account you're moving money to or from. Depending on if you entered a debit or credit on the first line, enter the same amount in the opposite column.
5. Check the amounts - you should have the same amount in the Credit column on one line and the Debit column on the other. This means the accounts are in balance.
6. Enter information in the memo section so you know why you made the journal entry.
7. Press Save and new or Save and close.

Moving forward, we'll need to record the payment in QuickBooks once your customer makes a payment on the invoice. This connects the payment transaction to the original invoice so your accounts stay balanced. To learn more about this one, check out this article: Record invoice payments in QuickBooks Online.

For tips and other resources, I’m attaching a link to access our Self-help articles. Simply click on the topic to view the detailed list of knowledge-based information.

I'd like to know how things going after trying the steps, as I want to ensure this is resolved for you. Just reply to this post and I'll get back to you. Take care always.