This is because Docker Desktop runs everything in a virtual machine. You can mount files info the virtual machine not everything and /dev/ is a special folder for special files to handle hardwares. I am not sure if it is even possible to mount it into a virtual machine, but if it is, you should check the Docker Desktop settings:
Preferences » Resources » File sharing.
I am on macOS now, but I believe it should be there on Linux too. If /dev is not in the list, then it tries to mount the device from the virtual machine which does not have it.
About contexts:
Without starting Docker Desktop, you run Docker CE.
I recommend you to remove either Docker CE or Docker Desktop to avoid confusion. I know, Docker says that you can run Docker CE and Desktop totegther, but in practice, it can be a problem especially if you don’t have a deeper knowledge about the two different softwares.