Support for Large BAR (16GB) on CW-NAS-WL

Technical Inquiry: Re-Size BAR / Above 4G Decoding Support for Intel Arc A770

Dear Support Team,
I am using your motherboard with an Intel Arc A770 (16GB VRAM) for AI workloads (LLM) under Proxmox/Linux.
To utilize the full potential of the GPU, I need to enable Resizable BAR (Re-Size BAR) and Above 4G Decoding to map the full 16GB VRAM address space.
Current Issue:
In the BIOS (Aptio Setup Utility), the "Above 4G Decoding" option is missing or disappears when the iGPU is disabled.
The "Prefetchable Memory Alignment" settings in the Chipset menu are capped at 31 bits (2GB), which is insufficient for a 16GB card.
As a result, Linux (lspci) only sees a 256MB BAR window, which severely limits performance and driver stability.
My Questions:
Is there a hidden BIOS menu or a specific key combination (e.g., Ctrl+F1) to unlock "Above 4G Decoding" and "Re-Size BAR"?
Is there a BIOS update available for this board that supports 64-bit BAR addressing for 16GB GPUs?
How can I manually force the PCIe Root Port (e.g., Port 9) to allow a 16GB memory aperture?
System Specs:
GPU: Intel Arc A770 16GB Limited Edition
BIOS Version:2.20.1276
ME FW Version: 12.0.47.1524 / Consumer SKU
Thank you for your technical assistance!

Best regards,
Sebastian Juch