I'm not sure since I haven't dug into the new features - but this sort of thing would be possible if tempo offset was a destination and could be assigned to a controller (superknob, assignable knob, etc). Something I've been wishing for - but tempo offset is something taken out vs. Motif. Not quite a "tempo track" - but to the limits of motion sequence - one could create a number of cycles to map out tempo changes over time and automate with the motion sequence feature.

Maybe there's still a different trick up the new features sleeve.

There is no TEMPO Track in the Pattern sequencer (Same as it was in the Motif XF, btw - there was no Tempo Track in Pattern Mode, you could add TEMPO CHANGE only after creating a linear structure, a Chain or after you converted the Chain to a linear Song).

In the MONTAGE/MODX all the PATTERN Scenes (sections) will share the same Tempo, exactly like in the Motif XF.
In the MONTAGE, the TEMPO is stored in the PERFORMANCE itself.

Tempo Tracks, in MIDI in general, must be outlined on a linear time line (it is the only way it would make any sense)...

Recording Real-Time Tempo Change
You can record real time Tempo Change in the MONTAGE/MODX MIDI (Song) Recorder (linear structure) -- you can even OVERDUB yourself adjusting the TEMPO of an already recorded linear Song. Just highlight the TEMPO parameter and record yourself changing tempo; Double tap TEMPO and you can punch in a specific TEMPO at a specific point while in OVERDUB record.

Is there any method to create a tempo track to have bpm changes along the pattern?

If you are working with PATTERNs they all will be at the same Tempo, only after you CHAIN them to a linear structure and then CONVERT TO SONG, can you automate (overdub) TEMPO change by recording it to the TEMPO Track.
Of course, you can manually adjust Tempo at ay time.

Reason it is not an option in Pattern has to do with the nature of how settings persist... you have a four Measure looping Scene. If you are using this to create a longer segment... your plan is to let it cycle 4 times creating a 16 Measure segment. If, at that point, you want to insert a Tempo change that ramps up over several measures to a new tempo... or changes immediately to a new tempo at the 17th Measure... How do you record that into the four Measure looping Scene... ?
It’s rhetorical... you don’t. There is no 17th Measure in a four Measure Phrase... you need to address Tempo Change on a linear timeline.
You are basically saying “...after the 4 measures finish playing four times through, change the tempo”

If you place the Tempo Change in the Loop, you’d need place it at very top on the fifth loop... (you’ve structured a linear timeline by the nature of the request).

You will notice you can manually change the Pattern Tempo by highlighting the Tempo box and spinning the Data Dial, or double tapping the Tempo box then type in the value- tap “Done” to active the change. Alternatively, you can slave the instrument to an external clock. Even feed clock control via the A/D Input. You can even tap tempo.

Using EXT TEMPO, is a viable way to work with Pattern Scenes, you can slave the MONTAGE to external clock and use an external device to control Tempo. If working with Scenes in a real time play situation, if you have a lot of specific Tempo Change requirements, simply explore the various methods of feeding external clock into the system.

Once the tempo changes, it persists, it will remain at the new tempo until it runs into another tempo command to change it. Tempo commands in looping sections is a conundrum.