Stool’s ability to float is usually related to air. A high fiber diet and gas can cause stool to float. A diet high in fiber leads to increased bacterial fermentation during digestion. This produces more air, which can get trapped in stool, causing it to float.

Source: https://www.medicalnewstoday.com/articles/325274

This same source says that too much fat could also cause floating, but from a different article:

Some people think that floating poop is caused by fat, but it’s usually caused by gas. Research has indicated that once floating stools were degassed, they weighed the same as sinking poop. This indicates that gas was responsible for making floating stools float, rather than fat inside the poop.

Source: https://www.webmd.com/digestive-disorders/what-to-know-about-floating-stools

But, in general, not necessarily something to worry about.