Two tasks at same time in QGIS Modeler

I am new to using the graphic modeler and I do not know how to do certain actions.

I have several treatments to perform on the basis of a buffer zone. Indeed, I have to polygonize 2 raster (which we will call A and B). After the polygonization of "A", other treatments follow each other using A. But after the treatment of "B", nothing continues. (I’ll let you see the diagram to better understand)

Currently, the polygonization treatments are one by one. Now, in order to save time, I would like the polygonization of A and B to be done at the same time, in parallel.

Do you know if it is possible to do this and, if yes, how?

If it’s possible only on Python, I can export the Modeler’s script and add the function.

<–What I have :<–What I would like to have.