Invoice Discount

1

Please i hope to add discount on the full amount of the invoice (I remember it was in old versions) There were two discounts
The first is a discount on the product. There is a discount column. A discount can be added to each product separately
The second was a discount on the entire bill

I need to add a discount on the entire sales invoice or Purchase invoice if possible

2

There was never the option you describe. A separate discount line item can be added. There is a Guide describing how to do that.