Explanation
The reason why the apply fails after adding a new provider to the configuration and immediately running terraform apply in the CD using the local backend is because Terraform needs to install the necessary plugins first. Terraform providers are plugins that Terraform uses to interact with various cloud services and other APIs. Each provider has a source address that determines where to download it from. When Terraform encounters a new provider in the configuration, it needs to run terraform init first to install the provider plugins in a local directory. Without the plugins, Terraform cannot communicate with the provider and perform the desired actions. References = [Provider Requirements], [Provider Installation]

Explanation
The correct way to reference an attribute from the vsphere_datacenter data source for use with the datacenter_id argument within the vsphere_folder resource in the following configuration is data.vsphere_datacenter.dc.id. This follows the syntax for accessing data source attributes, which is data.TYPE.NAME.ATTRIBUTE. In this case, the data source type is vsphere_datacenter, the data source name is dc, and the attribute we want to access is id. The other options are incorrect because they either use the wrong syntax, the wrong punctuation, or the wrong case. References = [Data Source: vsphere_datacenter],
[Data Source: vsphere_folder], [Expressions: Data Source References]

Terraform Cloud includes several features designed to enhance collaboration and infrastructure management. Two of these features are:
A web-based user interface (UI): This allows users to interact with Terraform Cloud through a browser, providing a centralized interface for managing Terraform configurations, state files, and workspaces.
Remote state storage: This feature enables users to store their Terraform state files remotely in Terraform Cloud, ensuring that state is safely backed up and can be accessed by team members as needed.

You do not need to use different Terraform commands depending on the cloud provider you use. Terraform commands are consistent across different providers, as they operate on the Terraform configuration files and state files, not on the provider APIs directly.

In Terraform Cloud, speculative plan runs are not automatically started when changes are merged or committed to the version control repository linked to a workspace. Instead, speculative plans are typically triggered as part of proposed changes in merge requests or pull requests to give an indication of what would happen if the changes were applied, without making any real changes to the infrastructure. Actual plan and apply operations in Terraform Cloud workspaces are usually triggered by specific events or configurations defined within the Terraform Cloud workspace settings.
References = This behavior is part of how Terraform Cloud integrates with version control systems and is documented in Terraform Cloud's usage guidelines and best practices, especially in the context of VCS-driven workflows.