What are some proper ways of doing rabbets in plywood with hand tools? I tried using a plough plane but it tore out the fibers too much.
What other manual options are there?
My best attempt was cutting with a thin saw the vertical cut (I used a mini Dozuki saw) followed by incisions from the side with a sharp chisel. It's important to set your depth of cut in a manner that it ends at the limit of a ply in the plywood. This will ensure a clean edge. Much cleaner than the plough plane.
I also used the chisel to clean ply leftovers a bit. The big improvement is that there is almost no tear-out at the top surface.