provider hashicorp/azurerm does not support resource type "azurerm_resource_group_policy_assignment

Hello Greencolor, seems like you already found a solution to your problem, I am just posting it here for ease of other folks who are facing similar issue on SO. Please feel free to add any points / your inputs to this if required.

As per the github link azurerm_resource_group_policy_assignment is supported by azurerm from the version = "3.49.0" so make sure youre using the version greater or equal to that.

Seems you're using the version = "2.52.0" is very outdated. As per the HarshiCorpdoc the latest version = "4.7.0" as of today.

As MarkoE suggested in always the best practice to use the latest version provider so that most up-to-date features, improvements, and security enhancements will be up-to date.

Refer: azurerm_resource_group_policy_assignment | Resources | hashicorp/azurerm | Terraform | Terraform Registry