Hi,

There is already a text column in journal items, called 'Label', which affects accounting reports. If you need a column for internal purposes, you can customize it. There are multiple ways to add a text field to journal items (invoice/bill lines) in Odoo.

1. By using Odoo Studio: 

Drag and drop the Text field where you want the column to appear.

2. By using Code

Python

from odoo import models, fields

class AccountMoveLine(models.Model):
    _inherit = 'account.move.line'

    x_text = fields.Text(string='Custom Text')

XML

<record id="view_move_form_custom" model="ir.ui.view">
  <field name="name">account.move.form.custom</field>
  <field name="model">account.move</field>
  <field name="inherit_id" ref="account.view_move_form"/>
  <field name="arch" type="xml">
    <xpath
            expr="//field[@name='line_ids']/tree/field[@name='name']" position="before">
      <field name="x_text"/>
    </xpath>
  </field>
</record>

Hope it helps.