Thank you for this report, Antoine, and sorry it did not work for you.
On the face of it you did very similar to the report by @smu44 (this month’s GS290 heroic white knight) in this post.
/e/ installé avec easy installer sur GS290... le téléphone ne démarre plus - #17 by smu44.
I would first look there for any possibility you took a wrong turn. I am sure you read the hazards of using SP Flash Tool incorrectly.
Bon chance
Edit on reflection, @anto you do not mention the charge status of your phone. This can be a difficulty at this point. It is important to have full or near full charge before attempting any rescue.