Google Cloud Storage Buckets should have a retention policy with retention period greater than or equal to 90 days (7776000 seconds). It is considered best practice to set a retention period of 90 days and it is often required for framework compliance or industry regulations.
In GCP Console -
In Terraform -
References:
https://cloud.google.com/storage/docs/using-bucket-lock
https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/storage_bucket#nested_retention_policy