Thank you very much for your answer.

I'm not familiar with the styleMaker and discovered it with interest.

It is indeed very powerful.
But ultimately my need concerns rather the "Style Creation Wizard" that I have also just discovered, with the idea of ​​configuring the wizard, so that the style generated for a given instrument only contains paterns with simply held chords or arpeggios ...

As the creation Wizard style does not allow it, I will therefore identify the styles containing these basic paterns, and use them to generate my midi tracks. I have already spotted the styles
SW44HELD.STY, HELDBOSA.STY for held agreements. I'll look for the arpeggios.

In any case, thank you for your invaluable help which made me progress in my search.