Now in Accounting, Odoo 15 provides features to generate 1099 reports with 1099 boxes.
Path Menu: Go to Accounting -> Configurations -> Accounting -> 1099 Boxes
Here, we can see some Boxes mentioned below with modules to generate CSV files of 1099 reports. Apart from that, we can add more 1099 Boxes.
For generating a CSV file of 1099 reports, we have demonstrated a path here.
Go to -> Accounting -> Reporting -> Management -> 1099 Report.
You can use the wizard to pick the start date and end date, also you need to select journal items and click on Generate button, after clicking, it will automatically check selected journal items and then generate a 1099 report CSV file with those journal items which are relevant.