In version 6.8.3, I get the following message:

│ Warning: Deprecated attribute
│
│ on repository_settings.tf line 18, in resource "github_repository" "repository_settings":
│ 18: private,
│
│ The attribute "private" is deprecated. Refer to the provider documentation
│ for details.

However, this deprecation is not documented by the provider documentation:

https://registry.terraform.io/providers/integrations/github/6.8.3/docs/resources/repository

Originally posted by @drmcclelland in #2569