A quick answer that is easy to apply because the weights are not absolutes but proportion of the person's weight:
Never, in anything less than an emergency, or lack of alternatives, and even then only for short distances, pack more than half your weight. It is possible to carry more, up to slightly over 100% of your weight, but you aren't going far or fast and at 50% to 100% the chances of injury go up.

(In most cases you will move more cargo faster with two trips at 50% than one trip at 100%. And you are far less likely to damage your back, knees, ankles.)

A third your weight is about the practical upper limit for most people to carry a pack any significant distance.

Anything more than a quarter your weight is tiresome.

A tenth your weight is about the upper limit of relatively unburdened backpacking where you won't be significantly slowed or tired.