On Mac → do NOT uninstall the YamahaSteinbergUSBAudio.kext under Library/Extensions → This will simply lead do uninstalling the Driver of your URxx Device!
To get rid of ONLY the Cubase Extension (UR Input Mixer inside of Cubase) delete the following file:
—> Macintosh HD ▸ Library ▸ Application Support ▸ Steinberg ▸ components ▸ ur44_extension.bundle
cheers