I first select a layer in a composition using OSC 'millumin/selectLayerWithName/xxx' , the opacity animation is taken into account when i select the composition.
If I put the composition on a board, that opacity modification is not taken into account.
I'm sorry, but you cannot control a layer that is inside an embed-composition (a composition in the dashboard, or a composition in another composition).
In brief : only the layers displayed in the list, can be accessed via OSC.
Yes, it's the same for the effects.
On the short term, no improvement in this direction is planned. On the long term, we might consider this, but I cannot guaratee it will come for sure.