A huge part of lifting things as a normal human is finger strength. 100lbs is fairly casual to support with your body if you bypass the need for fingers and don’t have to maneuver it. I have these furniture lifting straps that go over the base of your forearm (near elbow), go under the furniture like a wardrobe, then up to another person’s forearms. The was at which your forearms can lift feels like magic once you take the pain out of your fingers. I’ve used these with several people and all give the same response. I highly recommend getting them.

So while I’m not saying an arm could lift a car, many objects in our lives are movable because, at the upper limit, they’re kind of movable by humans already. I know you picked that weight at random, but the need for more of a brace than just the arm is more for the device’s own support rather than a limit of an average human body. And of course the size and shape of the object matters a lot too. But if it’s something where the weight can be supported well by your legs and core in some configuration, that’s not a lot of weight. Something like a pair of arms for equal support and a brace that extends to the waist would be manageable