It is doubtful, though, that the spotted fur, floppy ears, and other physical characteristics (domestication syndrome) are a result of the experiment [1]:
"The history of the Farm-Fox population undermines the commonly repeated narrative that a suite of domestication syndrome traits emerged solely as a result of selecting on tameness. There is no temporal link between most of the syndrome traits, which first appeared in Prince Edward Island (PEI) fur farms, and the later behavioral selection in Russia."
On the spotted fur [1]:
"The farm-fox breeders of PEI intentionally selected for white spotting and other unusual coat patterns (Figure 3). They noticed that crossing two white-marked foxes occasionally resulted in animals that held their heads askew, a phenomenon Belyaev would later describe in his population, suggesting shared genetic etiology. White spotting was more common in Belyaev’s selected than unselected populations, but has not been associated with less fearful behavior in individuals (Figure 2D)."
On the floppy ears [1]:
"The farm foxes of PEI occasionally had floppy ears, even as adults (Figure 3C). In the Farm-Fox Experiment, ‘delayed ear raising’ was noted (ears floppy past 3 weeks of age, but not necessarily into adulthood). While slightly more common in the selected population, the trait is extremely rare, and no association between delayed ear raising and less fearful behavior in individuals has been described (Figure 2D)."
[1] https://doi.org/10.1016/j.tree.2019.10.011