Hi,

For this i think you wont get an exact free module for the same. Still you can check this app in store, which merge same product lines in the sale order line, so in the report you wont have duplicated product lines.

See: Merge Same Product Line V9

The available version is v8 and V9, v11 is not available. Still you can try it in v11 with some changes. If you are not going to use any custom modules, you can inherit the report and make necessary changes accordingly.

Also there is issue while merging different lines, if the price is not given same in different lines.

For customizing the report, see this: How To Inherit And Modify Existing PDF Reports in Odoo

To port a module from one version to another: How To Migrate Odoo Modules To Another Version

Thanks