This problem occurred in the following environment:

NoMachine client on Windows 10
NoMachine server on macOS 11.4
Forwarded USB device: iPhone 14.4.2.

When the iPhone is forwarded via USB from the client machine to the server,  the iPhone shows up in the list of  connected USB devices on the client and it's marked with a green dot as if the forwarding is succesfully done. However,  it does not show up on the remote macOS side.

Forwarding a simple USB device like a mouse or USB disk works. If for example the USB disk is forwarded after the iPhone, it will also appear with a green dot but it will be not available on server side.