Welcome to the forum, Yann Beauvois.
If you're trying to delete an event created by Rainlendar in the same way a those in Google, then it's the same. But in you have unchecked the "repeat every" then you will have only 1 event. If the event have a recurrence, then the dialog for deletion will appear.
create an event
set in recurrence tab to repeat every 1 day and end after 5 occurrences.
after accept, right click on the event and click to delete this recently created event (click on the name)
If you do it right, then the delete dialog will appear.
EDIT: If you're trying to delete a Google Calendar event on Rainlendar, I don't use Google Calendar, but I suppose that the behaviour would be the same.