Hi @Yann F
You'll need to archive the card first before deleting it. Alternatively, if you want to add a "Delete" button to your board so you don't need to archive it first, you can do that with this Power-Up. https://trello.com/power-ups/5d0859bfbe10fe7460b4390a
I made a quick explainer video here to show you both methods :) https://www.youtube.com/watch?v=herIitK7xvM
Hope that helps,
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