Steinberg direct has a newer driver than listed for Montage M.  The newer driver (v3.1.7) advertises support for MacOS 15 where the Montage M download earlier driver only shows support up to 14.  Try that.

https://o.steinberg.net/en/support/downloads_hardware/yamaha_steinberg_usb_driver.html

Otherwise I would recommend not using the latest OS for music PCs because most electronic instrument manufacturers offer trailing support for new operating systems.  Meaning it could take a while before software catches up.  Sometimes you'll get a new computer pre installed with a bleeding edge OS.  Where you can do this, downgrading to n-1 (previous latest) is best.  Certainly if you have a PC or Mac with an older OS don't blindly upgrade the OS unless you know the upgrade will be "safe".  

Thanks for the help, Jason, but that driver doesn't work either.

Regards

Can't directly help any better than that suggestion.  I have a way to run MacOS 15 but no Montage M.   Maybe someone here or the other forum can chime in.

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Thanks Jason. I tried V3.1.7 , but no luck. At least not with the montage. Rolling back the OS system seems a little drastic, so I guess I'll have to wait for Yamaha to update the driver. 

Thanks

Tried V3.1.7 but no luck. And rolling back the OS seems a bit drastic, so I guess I'll just have to wait for Yamaha to fix the compatibility. 

@Yamaha: This is the 5th time I entered this reply. This website is so unstable.

Thanks Jason

Tried V3.1.7 but no luck. And rolling back the OS seems a bit drastic, so I guess I'll just have to wait for Yamaha to fix the compatibility. 

@Yamaha: This is the 5th time I entered this reply. This website is so unstable.

Thanks Jason

Can't remember if you tried switching MIDI modes between class compliant ("Generic" ) or proprietary ("Vendor" ).  After changing from one to the other I'd reboot the Mac and retry.

Thanks Jason. I tried V3.1.7 , but no luck. Rolling back the OS system seems a little drastic, so I guess I'll have to wait for Yamaha to update the driver. 

Thanks

Thanks Jason. I tried V3.1.7 , but no luck. Rolling back the OS system seems a little drastic, so I guess I'll have to wait for Yamaha to update the driver. 

Thanks