* config: The `list` and `map` functions, both of which were deprecated since Terraform v0.12, are now removed. You can replace uses of these functions with `tolist([...])` and `tomap({...})` respectively. [GH-26818]
* cli: Interrupting execution will now cause terraform to exit with a non-0 status. [GH-26738]
* backend/atlas: the `atlas` backend, which was deprecated since v0.12, has been removed. [GH-26651]
* config: Terraform will now emit a warning if you declare a `backend` block in a non-root module. Terraform has always ignored such declarations, but previously did so silently. This is a warning rather than an error only because it is sometimes convenient to temporarily use a root module as if it were a child module in order to test or debug its behavior separately from its main backend. [GH-26954]
* cli: The family of error messages with the summary "Invalid for_each argument" will now include some additional context about which external values contributed to the result. [GH-26747]
* cli: Typing an invalid top-level command, like `terraform destory` instead of `destroy`, will now print out a specific error message about the command being invalid, rather than just printing out the usual help directory. [GH-26967]
* provisioner/remote-exec: Can now run in a mode that expects the remote system to be running Windows and excuting commands using the Windows command interpreter, rather than a Unix-style shell. Specify the `target_platform` as `"windows"` in the `connection` block. [GH-26865]
* cli: Exit with an error if unable to gather input from the UI. For example, this may happen when running in a non-interactive environment but without `-input=false`. Previously Terraform would interpret these errors as empty strings, which could be confusing. [GH-26509]
