ELI5

The other examples about weight for construction are about avoiding long term settling of construction, not a single creatures weight. The overall point about weight per square inch are relevant, but let's take a simple example.

Cattle have a lot of weight on four feet that are smaller than a human foot. When they walk, one or two feet will be off the ground, and they don't sink unless it is muddy. Even then, it isna manner of inches and needs to be really wet. A horse running is putting multiple times their weight down and sideways on the ground and their feet aren't sinking in unless it is muddy.

An elephant has a ton of weight but a larger foot. Again, this relatively small footprint per weight does not let them sink into the ground unless muddy.

So if you are wondering how heavy a human sized character would need to be to sink into dry soil in a noticeable time frame while standing still then the weight would need to be many, many tons.

Depends on the type of soil. This site gives some general estimates:

Soil capacity is measured in pounds per square foot (psf). The load-bearing capacity of soils range from 4,000 psf for sedimentary rock to as little as 1,500 psf for clay and silt. Soils that are a predominantly sand or gravel typically fall in the middle, from 2,000-3,000 psf. In very few instances are actual soil tests done. Most inspectors will know the approximate soil-carrying capacity in the areas they cover.

depends how big their feet are! you'll estimate the bearing capacity of the soil (e.g. 100kPa), then divide weight by shoe area to get their pressure on the ground.