The execution plan for terraform apply will not be the same as the one you ran locally with terraform plan, if your teammate manually modified the infrastructure component you are working on. This is because Terraform will refresh the state file before applying any changes, and will detect any differences between the state and the real resources.

This command will initialize the new backend and prompt you to migrate the existing state file to the new location3. The other commands are not relevant for this task.

This command will upgrade the plugins to the latest acceptable version within the version constraints specified in the configuration. The other commands do not have an -upgrade option.

All of the statements are true of Terraform providers. Terraform providers are plugins that enable Terraform to interact with various APIs and services1. Anyone can write a Terraform provider, either as an individual or as part of a community2. HashiCorp maintains some providers, such as the AWS, Azure, and Google Cloud providers3. Cloud providers and infrastructure vendors can also write, maintain, or collaborate on Terraform providers, such as the VMware, Oracle, and Alibaba Cloud providers. References =
*1: Providers - Configuration Language | Terraform | HashiCorp Developer
*2: Plugin Development - How Terraform Works With Plugins | Terraform | HashiCorp Developer
*3: Terraform Registry
*: Terraform Registry

The terraform state file is locked when a Terraform operation that could write state is in progress. This prevents concurrent state operations that could corrupt the state. The forbidden actions when the state file is locked are those that could write state, such as terraform apply, terraform destroy, terraform refresh, terraform taint, terraform untaint, terraform import, and terraform state *. The terraform validate command is also forbidden, because it requires an initialized working directory with the state file. The allowed actions when the state file is locked are those that only read state, such as terraform plan, terraform show, terraform output, and terraform console. References = [State Locking] and [Command: validate]