Hello,
Use only _inherit,
- Remove the _name attribute and just extend the existing model. This is the most common approach when you just want to add fields to an existing model.
When you use both _name and _inherit, Odoo creates a new model that tries to use the same table names as the original model.
- Many2many fields automatically generate table names based on the model names, causing conflicts.
Hope this helps!
See also https://www.odoo.com/documentation/18.0/developer/reference/backend/orm.html#inheritance-and-extension