create a python toolbox with an existing python script

[GrégoireC]

Hello,

I would like to create a python toolbox, but in arcgis pro there is no longer the button to load the source script.

I wonder how i can define the source script ?

[DanPatterson]

Creating the toolbox is done in Arctoolbox, then you add a tool and specify the script there.

Can you show where the issue is?

[Luke_Pinner]

I think you are confusing a custom toolbox with a python toolbox.  You can't add existing scripts to a python toolbox, you need to edit it and write a Tool class.