I’m continuing the tests.
My Somfy roller shutters have been added in matterbridge, are correctly recognized in matterbridge and seen in Gladys :
However nothing visible in Matter devices :
EDIT: after disabling the Matter integration and re-enabling it, the roller shutters appeared!
and it works like a charm 
Opening:
And closing to 21%:
Well we get a slightly different result in the Tahoma mobile app, and I don’t know exactly what the matter-somfy plugin does:
Bravo @pierre-gilles, these advances are awesome!!
2 general remarks:
- it would be nice to have the % displayed on the slider (in general) because it’s a bit hard to aim precisely
- the control button should no longer be grayed-out (pressed) when you activate it (or when the command has finished). If we refresh the page, the gray goes away.