Hello Ws888,
Welcome to Microsoft Community.
If the MSFT Display Adapter V2s can be connected perfectly with the Surface Pro 7, then I believe that the MSFT Display Adapter V2s may not have hardware faults.
Then the problem is the compatibility between the MSFT Display Adapter V2s and Surface Pro 9, or you need to think about what reasons may affect the connection between the MSFT Display Adapter V2s and Surface Pro 9.
Since there are many possibilities, I recommend that you read the information in the following support links and follow the step-by-step instructions to check for these possibilities:
Troubleshooting Microsoft Wireless Display Adapter - Microsoft Support
If anything is unclear, please do not hesitate to let me know.
Best Regards,
Mitchell | Microsoft Community Support Specialist