I don’t see how you couldn’t learn both. Terraform is dead simple to learn and cloud formation is the best way to define your infrastructure in code in AWS. Even more wrapped by CDK. I don’t think you would go that far career wise knowing only with Terraform for IaC.

I also don’t understand those organisations that use every single AWS managed solution (RDS, Redis, Elasticsearch, EKS) but then they feel the need to manage their infrastructure state themselves with Terraform instead of choosing the managed solution for this.