I do not own a working food processor? Can I use a blender? Just by hand?

You can do this by hand. For the almonds, I might try using ground almonds (not almond flour). A little less than called for in the recipe. Cube and chill the butter, toss with the flour and other dry ingredients except the oats and almond meal. Using your thumb and fingers, squeeze the butter cubes into flakes, coated with the flour until integrated (roughly pea-sized crumbs). You can also use a pastry cutter for this if you have one. Toss in the oats and almond meal with a fork or your hands, and use to top the apple mixture per the recipe.

I would either chop the almonds alone in blender or by hand, or buy cut up.
Then mix the other ingredients in a bowl by hand or hand mixer.
If you do that in blender, it will be thick and hard to get out.
Don’t worry about texture - it’s uneven and ok that way.