Good evening Agathe and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
I would love to help you with this topic.
I believe you will find the answers you are looking for here: https://theeventscalendar.com/knowledgebase/using-one-license-live-dev-sites/
Simply put, you can move your license key around. Both of your sites will continue to work properly even when the license key is removed.
With that in mind, not having the license key in place will prevent you from doing “automatic” updates (from the wp-admin interface).
Let me know if that helps.
Have a great day!
Geoff B.
p.s.: we can totally continue this conversation in French if you prefer.