Hey there, @Charlietbh.

After thoroughly checking on my end, the option to view the Profit and Loss report by month is available in both classic view and modern view. Here's how you can adjust the report to display data by month:

For Classic view:

1. Navigate to Reports menu.
2. Open the Profit and Loss report.
3. Click the Customize button, and under Rows/Columns, select Months. 
4. Hit Run report.                                                  

For Modern view:

1. Navigate to Reports menu.
2. Open the Profit and Loss report.
3. Click the Display section, and under Display columns by, select Month.                                                   

Let us know if you need more help navigating QuickBooks Online.