If you are overweight enough that running carries a significant risk of joint issues then just walking at speed is likely to be enough cardio for you.

It is, it is so low-cost (running shoes) and available (walk out the door).

And doing it is close to the maximum calories you will burn per unit of effort and time.

Rucking will get you your cardio

Isn't this similarly hard on your joints to running, though, which is part of the problem with running when you're overweight? Or am I overestimating the joint impact?