Is straining cooked pasta from water a physical or chemical separation

It is a physical separation.

Only chemical separation involves the changing of substances and their bondings, which usually involves the use of heat or electricity. Meanwhile, physical changes does not require breaking the bonds of substances or changing a substance to another, common examples of physical separations are such as filtration or distillation.

Since straining pasta from water does not require breaking the pasta or water to other substances, plus heat and electricity is not involved, therefore this is a type of physical separation.