Connecting disconnected pieces in Fusion360 Stencil. Sketch entire model then extrude
As I see it, for a stencil you want the brown part with the white part(s) cut out.

This is easily doable. You can do this one sketch at a time, extrude it, and cut it out of the brown part.

To connect the inner brown parts to the rest of the brown, you'll need to cut a thin rectangle in the white character so that the inner brown pieces are connected to the outer brown pieces.