Does anyone know an easy workaround for payments and credits made after current invoice date not reflected in account summary on QBO invoices?

Glad to have you here on the Community page, @lfanaras.

Once you've included the account summary on your template, the payments or credits made after the current invoice date will show up beside the Payments and credits already applied to this invoice section with a negative account. The date under the Service Date column won't show the payment date but the service or invoice date. 

I've added these screenshots for your visual reference.

Let me know if you have any other questions. I'm always here to help. Have a good day!

On invoices,the summary is only showing payments through 12/31/2020, how do I get that date to show all payments made in 2021?

I can help you see all payments made in 2021, @Melissa1201.

Payments made after the invoice date will not show on the account summary. Account summaries only show charges and payments made before you created the invoice.

You can use a Balance Forward statement to show them their complete transaction history. Here's how:

1. Go to the Sales menu and select Customers.
2. Find the customer on the list and in the ACTION column, select the small arrow▼ icon, then Create Statement.
3. From the Statement Type▼ dropdown menu, select Balance Forward.
4. Enter the Statement Date, Start Date, and End Date.
5. Click on Print or preview or Save and send.

Check this article for more information about account summary: Add an account summary to an invoice in QuickBooks Online.

The following article will help you customize your financial reports in QuickBooks Online (QBO): Customize reports in QuickBooks Online.

Let me know if you still have questions about account summary. I'm always glad to help in any way I can. Have a great rest of the day!