Hello Cordelia,
Welcome to Microsoft Community.
I can understand that you have some doubts about the HDR function when using the Surface Pro 7, therefore please let me share some official information with you here:
High Dynamic Range (HDR) in Surface displays - Microsoft Community Hub
To be clear, the Surface Pro 7 does not support the use of HDR, as it only supports HDR video streaming. Currently, only the Surface Laptop Studio 2 supports HDR.
With the HDR Video streaming feature, you can support the playback of HDR videos in non-HDR display devices, you can learn more about this in the following support link:
Stream HDR video on Windows - Microsoft Support
Best Regards,
Mitchell | Microsoft Community Support Specialist