Hi TomerAdmon, Azure ARC essentially is used to simplify governance and management by delivering a consistent multi-cloud and on-premises management platform.
On the other hand, Azure Deployment Environments(ADE) empowers development teams to self-serve app infrastructure quickly and easily by using repeatable infrastructure-as-code templates, while ensuring adherence to enterprise governance framework. A deployment environment (app infrastructure) could be defined as a collection of Azure resources (PaaS, Serverless, IaaS, etc.) required to deploy and run applications.
Additionally, ADE provides comprehensive permission controls that can be leveraged to provide developers with the necessary permissions to create and destroy their own environments without providing broad contributor access to create resources outside the environment.
ADE will also be supporting cost management related capabilities such as the ability to centrally track and manage all environments across development teams and configure environments to auto-expire so that the resources are deleted once an environment is no longer needed.
Hope that helps, please let us know if there are any additional questions.