Terraform 'Error: Unsupported argument — An argument named "x" is not expected here' (or 'Unsupported block type') after terraform init -upgrade or a new provider major version. How do I fix it safely?

Cause: the argument or block exists in your configuration but not in the provider's schema that Terraform loaded. Most often a provider was upgraded to a new major version that renamed or removed arguments (or moved them into separate resources), because version constraints allowed it (no constraint, or >=), or a module was written for a different provider version. Other causes: a typo, or the argument belongs to a different resource type. Fix: 1. See which provider version is in use: terraform version and the .terraform.lock.hcl file show the selected versions. Compare with the version the configuration was written for. 2. Read the provider's upgrade guide and changelog for that major version (on the Terraform Registry); they list renamed and removed arguments and their replacements. 3. Pin providers deliberately in required_providers, e.g. version = "~> 5.0" to allow minor updates but not a new major, and commit .terraform.lock.hcl so everyone and CI use the same versions. 4. Either migrate the configuration to the new schema (following the upgrade guide, then terraform plan to check for unexpected changes), or pin back to the previous major (version = "~> 4.0"), run terraform init -upgrade to re-select, and plan the migration separately. 5. For modules, use a module version that supports your provider version, and pin module versions too. Verify: terraform validate passes, and terraform plan shows only the changes you expect (no surprise replacements). Sources: https://developer.hashicorp.com/terraform/language/providers/requirements https://developer.hashicorp.com/terraform/language/expressions/version-constraints