Terraform.tfvars - templating is not filled in

I included a terraform.tfvars file in my tfvars folder in a module, with multiple templating entries in it (i.e. expansion, aws_secrets, etc), and after running terraform build, in the resulting cache folder the file is copied exactly as is (with the templating syntax) into terraform.tfvars inside the module in .terraspace-cache.

Is somehow this filename protected and therefore the templating will not be run? Any help would be great!

Thanks!

UPDATE 25.6: I noticed that here you mention that only rb and tf files are processed - however we do see substitution in .tfvars files, not only in .tf files. I guess my main question is exactly which files are processed for expressions and which are not.