As with the quotation object, Linda uses the sandbox on which she tested the update to perform this test.
She continues with the Invoice object, with Axel at her side to see if the new page layout is of interest to the sales team.
Buttons
Linda isn't totally disoriented at the moment, noticing that the buttons are pretty much the same. There are only three different displays depending on the invoice status.
Draft invoice
In Draft status, directly after invoice creation, only these five buttons are displayed:

Invoice issued
If you issue the invoice by creating the PDF (Create PDF > Issue), two new buttons appear:

If you only issue the invoice by modifying the Status field, only the Generate accounting entry button will be displayed.
Linda notices tabs, it's all new around here!
She goes through them one by one.
Tab: Details
When the invoice is in status = Draft, the following fields are displayed:

However, when the invoice is in status = Issued, the Reference field appears with its reference name:

Reminder: Invoice numbering regulations are detailed in this article from our knowledge base: Invoice numbering.
Tab: Presentation
These fields concern the entire display of the invoice PDF, either they are displayed on the PDF like the fields in the first column, or they manage the optional display, like the second column. You will find a complete list of fields in this article: Field Dictionary.
Tab: Amounts, Discounts & Special terms
In the Discount and Special terms section, the Discount reason field is only displayed if you have filled in the Discount rate field.

Tab: Recovery
This section is hidden when the invoice is in status = Draft, like this:

Note: you can of course add fields to your page layout.
However, all fields appear when the invoice is in status = Issued. This is the display for an invoice paid without dunning.

Tab: Related objects
As with the quotation, this tab shows the links between your invoice and an opportunity or quotation, if the invoice has been created or linked to a record of one of these two objects. The same applies to accounting data.
If the invoice is part of a schedule generated from a subscription, you will also find the information from this record.

The Initial invoice field is added if the invoice type is Credit Note:

Note: This field links to the invoice to which the cancellation or refund relates.