You are absolutely right.
It should be available from http://download.yamaha.com/ .
At this moment only 1.20 is available.

Strange, for I have downloaded and installed 1,50 a couple of weeks ago successfully.
(After waiting for s few days, to see if problems would arise. I didn't read about that.)
Perhaps they are working on a 1.51 version?

(In that case they can turn on the light for any transposed settings, and not just the octave)

Hello Benjamin and Jan - I just checked too - and Update 1.50 has disappeared from the download site. This does not bode well for those using 1.50? I have a couple of issues - wonder if Yamaha have pulled it to put it right? Sure hope so! Power to your elbow, Yamaha! Do you know anything about this, BM?

Please refer to the hint shown in red ...

https://europe.yamaha.com/en/products/music_production/synthesizers/montage/features.html#product-tabs

Looks like a corner case resulting in a "bad build" type release. It's worth repeating the messaging here:

Copied from https://europe.yamaha.com/en/products/music_production/synthesizers/montage/features.html#product-tabs :

Important notice about MONTAGE OS v1.5:

There is an issue related to the power on sequence in MONTAGE OS v1.5. As a result, we are suspending MONTAGE OS v1.5 downloads.
We are also working on an update to fix this issue. This update (MONTAGE OS v1.51) will be available around Mar 10.

If you already installed MONTAGE OS v1.5, please note the following information. If you turn the power OFF during the power on sequence, there is a small chance you could lose all sound. To avoid this situation, please do not turn off MONTAGE during the power on sequence.
If you encounter any problems, please contact your customer support center.
We apologize for any problems this may cause.