Hello MDIW,
Welcome to Microsoft Community.
You don't need to connect both, just one that can connect to one of the USB-C ports. Let me introduce you to the Surface's dedicated Dock, Thunderbolt™ 4 Dock:
Buy Surface Thunderbolt™ 4 Dock (Ports, Compatibility, Price) - Microsoft Store
Or, another docking station that doesn't extend with USB-C, Surface Dock 2:
****Buy Microsoft Surface Dock 2 – Microsoft Surface
Both Microsoft docks support the Surface Pro 9, and they have the most perfect compatibility with the Surface.
Best Regards,
Mitchell | Microsoft Community Support Specialist