Welcome to the Community, @aislinggarton.

In QuickBooks Online (QBO), the ability to view or run a Profit and Loss by Class month by month report is currently unavailable. You can filter the report by each month and export it to Excel as a workaround. This can be done by clicking the Export (between Print and Gear) icon at the top right. Then select Export to Excel.

For more information, please refer to this article: Export your reports to Excel from QuickBooks Online.

I'll pass along your suggestion to our Product Developers. They're always looking for ideas to consider on how to improve QBO. In the meantime, I recommend visiting our Blog site. This is where we share recent happenings and future developments, such as updates to newly added features.

Please leave a comment below if you have any issues or concerns. I'll be here to help. Have a good one!