I can help to clarify why the P&L is acting as you've explained. When Customizing a Profit and Loss and filtering it to customers, it will only display transactions assigned specifically to those individuals. This means only Billable Expenses assigned to the selected customers will display in the report as you've described it. Since most expenses aren't appearing after filtering this way, they haven't been created as Billable. You'll have a few options for reporting your P&L in this way:
1. Profit and Loss by Customer Report
From QuickBooks Online, navigate to the Reports tab.
In the search bar, type Profit and select Profit and Loss by Customer.
This report sorts customers into columns, displaying their income for each of the Profit categories.
Please note, the expenses still won't be displayed per customer unless they're assigned in a Billable transaction. However, the total expenses (as compared to the regular P&L for the same date range) will remain the same in the Total Expenses section. Here's a screenshot displaying how the P&L by Customer reports:
2. Profit and Loss Detail sorted by customer
Follow the steps above to search for the Profit and Loss Detail report.
This statement displays each transaction in all included income categories.
You can sort each of these transaction groups by customer by clicking the Sort dropdown (▼) and selecting Name.
This method also groups the fully listed expenses by Vendor in the bottom half of the statement. The image here shows what the report looks like:
3. Assign customers to those expenses and make them Billable
If you haven't already, enable Billable Expenses by clicking the Gear icon (⚙) > Account and Settings > Expenses tab > Check the box to Make expenses and items billable.
On the unfiltered P&L report, click on each expense category to open it and select a transaction to review it.
Make sure there is a name assigned under the Customer column of each Check,Expense, and Bill that you review.
The methods above enable you to have your P&L sorted by customer while including necessary expenses. In addition to all of these resources, we also offer a guide on customizing your Profit and Loss that's worth checking out. Please let me know if you have any additional questions or concerns. Thanks for coming to the Community, wishing you continued success.