Can’t know for sure without an inspection, but here are a few possibilities. You could have aggressive brake pads that bite hard with very little pedal pressure. You could have an issue with the brake master cylinder or brake lines that are causing excessive brake pressure. You could have a bad engine mount or control arm bushing that causes excessive motion when braking, but I think this is less likely. You could also potentially have a caliper that is starting to seize. If it’s the caliper, a rebuild or replacement may be necessary.

Does it feel like the jerking is coming from the braking system or the powertrain? Does the vehicle still jerk when you let off the throttle and don’t apply brakes?