Steinberg released the latest Yamaha USB-MIDI driver (V1.5.0): Yamaha USB-MIDI Driver V1.5.0 · 4.7 MB
It has to be installed on top of TOOLS for CC121: TOOLS for CC121 1.7.7 · 4.7 MB
More info: CC121 | Steinberg
I’m confirming everything works for me after installing the driver (Cubase 10.5.30 on Mac M1 with Big Sur)! 
