Split routine with free weights, nothing too fancy. I would not feel comfortable doing squats because I cannot hold the bar, best I could do would be leg press.
It is possible to
squat with one arm, but it is fairly risky. You would definitely need bumper plates in case the weight slipped off and crashed to the floor. However, you'd probably be better off doing whatever you can
safely and recovering any strength losses once you are healed. Many of the heavy, full body motions are probably a no-go with one arm, but here are still plenty of other exercises you can try: lunges, step-ups, split squats, air squats, jump training (long jump, high jump, box jumps), one legged squats, sit-ups, back extensions, and running/sprinting. You can also work on one arm dumbbell/kettlebell versions of most exercises, including snatches, cleans, press, jerk, rows, etc. This will develop your core & stability and iirc, many of the neurological benefits will actually apply to the injured arm once it is out of the cast.