The tfr protocol supports a shorthand notation where the REGISTRY_HOST can be omitted to default to the public registry (registry.terraform.io) if you use tfr:/// (note the three /). For example, the following will fetch the terraform-aws-modules/vpc/aws module from the public registry: tfr:///terraform-aws-modules/vpc/aws?version=3.3.0.
Describe the solution you'd like Improve handling of shorthand TFR urls in case of OpenTofu to allow usage of OpenTofu registry.
Describe alternatives you've considered N/A
Additional context
https://terragrunt.gruntwork.io/docs/reference/config-blocks-and-attributes/
https://github.com/gruntwork-io/terragrunt/blob/master/options/options.go#L526