You can automate both Terraform and Pulumi in a similar way to Atlantis using Spacelift[0] (though generally with a lot of additional features and customizability thrown in vs Atlantis; but you can also accomplish basically the exact Atlantis flow).

It's a CI/CD system specialized in Infrastructure-as-Code.

[0]: https://spacelift.io

Disclaimer: Software Engineer at Spacelift, though I'm recommending it not just because I work there, but because I think it's legitimately a very good product.