USB Midi out - no midi signal

I’m having the same issue. There is no usb option on my midi screen. I’m wondering If I did something when I erased an internal expansion file. Everything is fine besides and it connects and works in controller mode.

it's down to hardware - key37 have an additional usb controller while all other ones have one chip only, which is controlled by usb mux. USB cannot work as Host and Peripheral at the same time and since in standalone mode usbmux is switched into "host mode" (to be able manage anything connected to one of the 'A' ports), it cannot negotiate any connection with another host (ie. Ableton which is another host managed by operating system - Windows/Mac/Linux).
In other words:
USB = HOST <-> PERIPHERAL

USB != HOST <-> HOST / USB != PERIPHERAL <-> PERIPHERAL