Integrating sustainability into green supply chains is essential for balancing environmental and economic goals. This paper presents a computational system dynamics model that optimizes the green supply chain design and operational efficiency within omnichannel retailing. The model integrates five interrelated sub-systems: physical stores, distribution hubs, hybrid facilities, facility integration, and eco-financial metrics, to analyze interactions between inventory management, carbon emissions, and operational performance. The study evaluates various scenarios based on product characteristics, market conditions, and the transformation from traditional to digital retail. Comprehensive validation, including behavioral analysis and extreme condition testing, validates the model's real-world reliability. The results indicate that higher rates of omnichannel transformation generally enhance profitability across most product categories, though their environmental impact is less consistent. In some scenarios, carbon emissions decline; in others, they remain unchanged or even rise. Affordable necessities and long-lasting goods tend to achieve profit growth alongside stable or reduced emissions. High-end products also maintain profitability, typically without substantial environmental compromises. By contrast, small-format products show mixed financial and ecological outcomes, pointing to the influence of additional, context-specific factors. The insights provide a strategic framework for businesses and policymakers to optimize omnichannel integration, balancing profitability with sustainability in green supply chain networks.