Aloha and bonjour mom ami. 
First off the sale man is wrong.
The physical ‘DIN’ connector that musicians call a ‘MIDI plug’ IS
showing up less in todays gear in favor of the USB
connector but the MIDI language used by both is still the same.
So MIDI is not dead. Just the connector (possibly).
My GR55 guitar synth uses a MIDI USB connector and
plugs directly into my computer USB port.
As I perform, the GR sends MIDI info via USB that is then ‘read/seen’ by Cubase.
Your Yamaha D/Piano should work the same way.
So
1-plug your keyboard directly into your computer’s USB port.
Cubase should ‘see’ that.
2-plug the audio outs of the keyboard into the UR28M and then go from it’s USB port
into a second USB port on your computer
Cubase should also ‘see’ that.
and bob’s yer uncle’.
{‘-’}