All can see here on the XPS 13 7390 2-in-1 driver page that only Windows 10 is validated and supported by Dell.   The fact that the webcam functions in the validated and supported Windows 10 indicates the hardware is working fine.   In regards to the out of scope Fedora OS, you will need to refer to an online Fedora OS support forum.
I've tried a few distributions and am now on Fedora 31. Once `modprobe.blacklist=intel_lpss_pci` is added to boot options, the laptop mostly works. The webcam, however, does not work and isn't listed via:  
7390 2-in-1 Linux, Webcam not working