Hi,

In Odoo, if the bank account field is greyed out (read-only) on the invoice.

Here's how the system works:

    Customer Invoices (account.move with type out_invoice)

        The bank account shown is generally taken from:

            The Customer’s “Bank Accounts” tab (res.partner.bank) – if present.

            Or from the Company’s bank account, printed on the invoice template.

    The Bank Account Field (if visible) is usually not editable directly on the invoice form unless:

        You’re editing a vendor bill (not a customer invoice).

        Or you have customized the view to make the field editable.

There may be any customisation in the field that causes the non-editing option for the bank account.

To make the field editable, try the following code.

<field name="partner_bank_id" readonly="0"/>

Hope it helps