Hey Kenneth,
this is the expected behaviour. The internal Raspberry Pi 3B has neither the resources nor the drivers installed to render the 3D toolpath simulation. It is only shown on a remote computer. The “Upload” icon of the Onefinity User Interface, when opened on the remote computer, shows the “File open…” dialog of your remote web browser which allows access to your remote computer’s entire filesystem.
I access the buildbotics-derived Onefinity controller the same way, over an ethernet cable connected to an ethernet switch.
In the controller in /etc/network/interfaces.d/eth0, I have set up a ip address from the private ip range so it is accessible from any computer in my local network.