Industrial Internet of Things (IIoT) architectures are becoming central to Saudi Arabia's digital manufacturing agenda because connected sensors, programmable logic controllers, robotics, manufacturing execution systems, digital twins and cloud analytics can raise productivity, quality and energy efficiency. The same connectivity, however, expands the cyber-physical attack surface of factories that were historically protected by isolation and proprietary protocols. This review develops a cybersecure IIoT architecture model for Saudi Arabia's digital manufacturing ecosystem under Vision 2030. It synthesizes recent literature and standards published between 2020 and 2025, with emphasis on predictive cybersecurity, zero-trust principles, operational technology segmentation, machine-learning-enabled anomaly detection, governance and incident response. A narrative review methodology is used to classify threats, architectural controls, implementation barriers and research gaps. The analysis shows that resilient digital factories require more than perimeter firewalls; they require asset visibility, identity-based access, secure conduits between IT and OT, edge-level monitoring, explainable detection models, supplier assurance and safety-aware recovery playbooks. The paper proposes a layered architecture and risk-scoring cycle that can be adapted by Saudi manufacturers, industrial cities and giga-project supply chains. It concludes that Saudi digital manufacturing can achieve high-trust automation when cybersecurity is designed as an operational capability, not added after deployment.