Highlights:

Looks like transport controls are added this time around.
There are many (512) new preset performances added - lots of ones I recognize from the past. As such, there's a Live Set of "Motif XF" Performances.
The waveform editor is slowly adding items useful for on-Montage building your own elements with custom samples.

Release notes:

Fixes and Enhancemenets

New features;

New Performances have been added.
The DAW Remote function has been added.
A new function has been added that allows you to selectively enable (or disable) recording of Arpeggio data, when recording MIDI songs.
You can now set a Center note in the Edit Waveform display.
You can now set a key for assignment when loading WAV files or AIFF files as waveforms.
You can now select the Assignable Knob for Common Parts, by pressing the [PART COMMON] in the dialog displayed when selecting the Part parameter and pressing the [CONTROL ASSIGN] button.
The Panel Lock function has been added to prevent inadvertent operations during your performance.
Fixed problems;

Fixed a problem in which the footswitch would freeze when it's used as a sostenuto in combination with the sustain pedal.
Fixed other minor problems.

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You can check out the article: https://www.yamahasynth.com/montage-category/montage-os-v2-5-new-feature