Hello, Maîtresse Célia!
Unfortunately, the Slider can be shown only in the single Post/Page.
But, luckily for you, if you want to show a Slider on your category page there is a workaround :
Use the Elementor Page builder to create a new page for your custom post Category then use the Gold Addons “Blog” widget (the plugin we suggest to install with our theme) to insert the blog posts on your page.
https://prnt.sc/nmgbgy
The Gold Addons Blog widget has the option to set the view for the Blog post based on category.
https://prnt.sc/nmgb1m
Insert the (GA) Blog widget to every page you want to show the blog posts, then edit the (GA)Blog element and change a different Blog category for each Page from the “Content” tab.
In that case, you will be able to add a Slider to your page (from the “Agama Optons” meta box)
http://docs.theme-vision.com/article/setup-agama-slider/
Regards