do you have any Custom module Installed?

It seams like you don't have access rights to Validate Picking.

if you need to modify Done Quantity, Edit (Modifier in French) Picking and click on the button Icon on the most right of your order line.

If you need to put products in packages, click on button in Order Line and Create  Destination Package if you need to pack some products accordingly

If you need to pack all products in one pack just Click on the button in Order line and set done quantity for all your products, then click on put in pack (FAIRE LES COLIS in French) button.

so it is not active button? or you get an error? lot/serial you have entered with qty?

Sure, sorry it's all in French

- here is where I should see the "validate" button: https://ibb.co/XVYvyk4 (instead, I have a button that allows me to block the order, but I don't want to do that)

- I don't have any way to modify the "Done" column ("Fait" in French) so I don't know how to proceed

At the bottom of the page I have an empty list "make the packages" but when I click it says I should first indicate the quantity that I want to put in the packages. I have no idea how to do that and read some doc saying that it was not compulsory, so I don't think that there is an issue there. 

Hi marie, 

can you take a screenshot of your problem so that we can better understand your problem

Best regards