Thank you for reaching out regarding the issue you are experiencing with your management reports in QuickBooks Online, @jayeh. I understand that you would like to include comparisons in your reports, and I'm here to assist you.

As I've replicated your concern here on my end, running a Profit and Loss and Balance sheet comparison report requires specific customizations to ensure data are showing accurately on the report.

To enable the comparison feature and include previous year or previous period data in your reports, please follow these steps:
 

1. Navigate to the Reports tab in QuickBooks Online.
2. Select the Management  reports tab.
3. Look for the specific report under your management reports, such as the Balance Sheet or P&L report.
4. Click on the report to open it.
5. Once the report is open, locate the Reports and Chart page.
6. On the Reports and Chart page, you will find checkboxes or options to enable comparisons.
7. Check the box that allows you to compare the report with the previous year or previous period, depending on your desired comparison.
8. Save the changes you made to the report settings.
9. Re-run the report, and the comparisons from the previous year or previous period should now be included.

See screenshot below for your visual reference. 

I'll include this article for more details: View and edit management reports in QuickBooks Online

Moreover, you'll want to memorize the data added to your reports to save current modifications made from them. It also includes insights on how to set schedules and email information for a memorized report.
 

Your success in running reports with QuickBooks is our top priority. We're always here to help.