Hi @Emeric_Petitgenet
Welcome to MongoDB forums!
From the error message, it seems to be a DNS issue - the SRV record resolution is failing. Please check your DNS configuration. You can try to perform a nslookup to manually check DNS resolution.
Additionally, you can cross check by connecting to your Atlas cluster with the same URI on the same machine, via mongosh or MongoDB Compass.
We also published a MongoDB Atlas + Symfony step by step tutorial that should help you as well - https://www.mongodb.com/developer/products/mongodb/mongodb-php-symfony-rental-workshop/