Welcome to the Community. I'm here to provide clarification about the report you need in QuickBooks Online.
Currently, the option to run a stock aging report in the Online version is unavailable. You'll need Enterprise in QuickBooks Desktop to run a report like Inventory Aging Summary.
I know how essential the report is for QuickBooks users. It helps identify slow-moving or obsolete inventory that needs to be revalued to correctly calculate your cost of goods sold.
For now, I recommend sharing your ideas with our product engineers. We continue to improve the product and this suggestion may be considered in future updates.
Here's how:
Click the Gear icon in the upper-right corner.
Select Feedback under Profile.
Share your feedback.
Hit Next to submit.
Also, the reports in the Online version are customizable. I've attached an article I find helpful in personalizing report data, as well as how to export them to Excel or PDF: Customise reports in QuickBooks Online.
Leave a comment below if you have other concerns related to the reports or the QuickBooks features. I'll be happy to help you some more.