The rapid expansion of artificial intelligence workloads and machine-to-machine traffic necessitates flexible, on-demand lightpath provisioning in optical transport architectures. The industry is shifting toward disaggregated, multi-vendor environments where the Open Optical Line System (O-OLS) is decoupled from third-party Open Optical Terminals (O-OT). Here, the Optical Network Digital Twin (ONDT) emerges as a critical enabler for real-time Quality of Transmission (QoT) estimation and automated control. However, a significant barrier in multi-domain scenarios is computing End-to-End (E2E) performance without disclosing proprietary physical topology details to adjacent domains. Furthermore, to address escalating traffic demands, the industry is adopting multi-band transmission as a near-to-mid-term solution.