The UVC 4K driver for the THETA V is compliant with UVC 1.5. However, I do not think it supports the entire UVC 1.5 specification.
I do not know about control under the .NET environment.
A community member is using Windows 10 with direct show to get the modes and KS_H264VIDEOINFO for debugging.
The community does not have a lot of information on this, so you would be forging new ground.
If you’re just trying to push an email, can you using the normal WiFi API or the USB API?