I can assist you in generating a report that displays the total vendor cost per month transaction list in QuickBooks Online (QBO).
While it is possible to run reports for vendor costs, it requires manual customization, and you have to click on the amount in the report to identify the vendors.
Afterward, you can export the report to consolidate the data.
Here's how you export the following reports and lists into individual Excel files to export your report or list:
Go to Settings ⚙.
Select Export data.
On the Reports tab, set the date range.
Add or remove items from the Reports and Lists tabs by turning the switch on or off.
Select Export to Excel.
You'll be prompted with confirmation that the data has been exported.
Additional guidance when running reports is also given in these articles: