The problem I was encountering was because my variables started with "default_", changing them resolved the issue in my case.

Hello Daniel, I'll help you set up the Many2one fields in res.config.settings correctly.

  The error occurs because Odoo attempts to write the value of default_pricelist_company and default_pricelist_individual directly to a field named pricelist_company and pricelist_individual on the res.partner model, which do not exist.

  Remove the default_model='res.partner' from your field definitions. This attribute is not needed and causes Odoo to look for corresponding fields on res.partner.

  Instead of relying on default_model, you will need to create a function that applies the pricelist based on the configuration when a partner is created or updated. This can be achieved by inheriting the create and write methods of res.partner.

  Here's an example of how you might structure your res.config.settings model:
  ```python
  class ResConfigSettings(models.TransientModel):
    _inherit = 'res.config.settings'

    default_pricelist_company = fields.Many2one(
        'product.pricelist',
        string="Default Pricelist for Companies",
        config_parameter='my_addon.default_pricelist_company'
    )
    default_pricelist_individual = fields.Many2one(
        'product.pricelist',
        string="Default Pricelist for Individuals",
        config_parameter='my_addon.default_pricelist_individual'
    )
  ```

  Then, in your res.partner model, override the create and write methods to apply the pricelists:
  ```python
  class ResPartner(models.Model):
    _inherit = 'res.partner'

    @api.model
    def create(self, vals):
        partner = super(ResPartner, self).create(vals)
        self._set_default_pricelist(partner)
     &

Change your field  name from default_pricelist_company to pricelist_company_default

Because if you set the first name of your field name by default, it will raise this error