Hello, Dominique de Mezieres.
Welcome to Microsoft Community!
If you wish to install drivers for USB to RS232 on Surface Pro 11, you need to make sure that the drivers provided are compatible with the ARM system architecture.
The Surface Pro 11 utilizes a Snapdragon X CPU for lower power consumption and higher performance, and there are differences between this model and Intel, resulting in an ARM system architecture.
Therefore, you can check with the driver vendor to see if they offer a version of the driver for ARM. Or you can search to find more ARM drivers to download.
Additionally, you can also try to manually get the driver and firmware installer for Surface Pro 11 to troubleshoot potential driver issues and maintain device performance:
Download Surface Pro 11th Edition Drivers and Firmware from Official Microsoft Download Center
These are some of the information I can share with you at this time.
I am sure when you have the right compatibility you will be able to run them well.
I am here to wish you a Merry Christmas.
Best Regards.
Leo.L - Microsoft Community Support Specialist