The correct answer is Heterogeneous infrastructures across public cloud, on-premise, and IoT devices.

Heterogeneous infrastructures across public cloud, on-premise, and IoT devices is the major difficulty because these environments expose widely different management interfaces, operating systems, and device capabilities. Each class of system may require different configuration formats and tooling, and that makes it hard to apply a single secure configuration baseline consistently.

The diversity in heterogeneous infrastructures across public cloud, on-premise, and IoT devices also creates testing and validation challenges. Changes that are safe in one environment can break another, and some IoT devices lack the resources to run standard configuration agents or receive frequent patches, so organizations must design multiple controls and processes to cover all systems.

Inconsistent policy enforcement across multiple cloud projects is not the best choice because that problem is largely scoped to cloud governance and can be mitigated with centralized policy tools and organization level controls. It is a real challenge but it does not capture the full scope of mixed on‑premise and IoT systems.

Google Cloud Deployment Manager is not correct because it is a specific infrastructure as code tool rather than a fundamental difficulty. It applies mainly to Google Cloud deployments and does not describe the broader problem of coordinating secure configurations across many different platforms.

Many users granted identical roles is also incorrect because that describes an identity and access management issue. It is important for security but it is distinct from the operational and technical complexity of maintaining consistent secure configurations across diverse infrastructure types.

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