It's great to see you're already getting started on your year-end reporting. I see the PIER report is one used to ensure that your numbers are correct for year end so you can complete tasks like issuing T4s, as you've mentioned. I'd be happy to help you find the details you need in QuickBooks Online for your payroll calculations.
At QuickBooks, we know how important year-end tasks are, which is why we've created guides such as the QuickBooks Online Payroll Year-end article to help you work through it. One of the steps mentioned in this article, under the section Before the first payroll of 2021, is to run payroll reports to make sure your information is correct.
While there isn't a PIER report specifically, there are other reports in QuickBooks Online that can show you deductions and other such details. Reports such as the Employee details, Payroll details, and the Payroll Taxes and Wage Summary reports can be an asset. If those aren't quite showing you the information you're looking for, there are a number of other payroll reports you can review as well. These two articles can help.