IMHO it should be possible to double the weight/strength ratio, or cut the strength/weight ratio in half, without too much extra strain on someone.
A person of average height who weighs twice as much as an average person would have twice the stress on his muscles and bones. And I know such a man who took walks up to about 8,000 feet (2.4 kilometers) before he lost a lot of weight. Some humans who have twice as much weight as normal persons of their height can function in modern society, even if they would be less successful in a hunter-gatherer society where more activity was required.
If someone six feet (1.82 meters) tall weighing 180 pounds (81.64 kilograms) is doubled in dimensions, he will be twelve feet (3.65 meters) tall and weigh eight times as much, or 1440 pounds (653 kilograms). His bones and muscles would have twice the dimensions and thus four time the cross section area as before, and would have to support eight times the weight, and thus have twice the weight stress as before.
And if that is roughly equivalent of a man six feet (1.82 meters) tall weighing 360 pounds (163 kilograms), then the double dimension twelve foot tall man should be able to function reasonably well.
but on the other hand, it is hard to find evidence to support the idea that a man that tall would function well. There have been a number of men over seven feet (2.13 meters) tall due to their genes, and many of them were quite strong. But most men and women who were extremely tall were so because of abnormal medical conditions, and did not function well, and had health problems.
The Guinness Book of World Records lists the Scottish-Canadian giant Angus MacAskill (1825-1863) as the tallest non-pathological giant, and the strongest man who ever lived. He was 7 feet 7 inches (2.31 meters) tall.
On a third hand, there are legends of even taller men who were reasonably strong and healthy.
The Philistine warrior Goliath was described as "four cubits and a span" (6 feet 9 inches, or 2.06 meters) or less plausibly as "six cubits and a span" (9 feet 9 inches, or 2.97 meters).
Georgios Maniakes was a famous eastern Roman or "Byzantine" general in about 1030 to 1043 who was alleged to have been eight feet (2.43 meters) tall.
The Roman emperor Maximinus (c. 173-238) was a Thraco-Roman peasant from Moesia (in the region of modern Serbia & Bulgaria) who joined the Roman army and usurped the throne in 235 and was killed in 238 aged about 65. Maximinus was allegedly super strong and eight and a half feet (2.59 meters) tall.
On a fourth hand, every human proven to be over 7 feet 7 inches (2.31 meters) tall, and some shorter than that, reached their height due to pathological conditions and most of those were unhealthy and had various size related medical problems.
On a fifth hand, there was the Giant of Castelnau. Three bone fragments were excavated in a bronze age cemetery in Castelnau-le-Lez, France, in 1890. They were estimated to be from a human about 3.50 meters (11 feet 6 inches) tall. If that is correct, that person would have been healthy enough and lived long enough to grow very long bones in a prehistoric era.
On a sixth hand, there was the extinct ape genus Gigantopithecus which may have walked on two legs or four legs. Some scientists believe that they were about 1.8-2 meters (5.9-6.6 feet) tall and weighed 180-300 kilograms (400-660 pounds). Other scientists believe they might have been much larger, standing up to 3 meters (9.8 feet) tall and weighed up to 540-600 kilograms (1,190-1,320 pounds). They are popularly imagined to be up to 12 feet tall. But Gigantopithecus almost certainly didn't have human body proportions anyway.
I suggest that you study the lists of the tallest humans who ever lived and then find out about the health problems many of them faced.
And possibly also study the lists of heaviest humans and find out about their health problems.
It seems to me that if a group of humans become genetically adapted or scientifically modified to change their proportions to better fit their size, they could be healthy in gravity similar to Earth's gravity with average heights of about seven feet (2.13 meters), eight feet (2.43 meters), nine feet (2.74 meters), etc, and still look fairly similar to normal sized humans with only slightly different proportions.
But it seems much less plausible to me that humans living in a one Earth gravity environment could be twelve feet (3.65 meters), or eighteen feet (5.48 meters), or twenty four feet (7.31 meters) tall, and still closely resemble normal sized humans.