Dear @PierreAllain
If you need a Video Thumbnail to work within your Carousel:
In your Carousel select the same video that you are using for Video Thumbnail:
Screen Shot 2021-02-02 at 4.44.03 PM.png
Then Clicking on the element and selecting "Edit Link" - Link to the Project you wish.
I hope this helps you and the function that you needed is there :)
Best
Richard