“A squircle is a shape intermediate between a square and a circle. There are at least two definitions of "squircle" in use, the most common of which is based on the superellipse.”
So, squircle isn’t tightly defined.
It also says: “Apple uses an approximation of a squircle (actually a quintic superellipse) for icons in iOS, iPadOS, macOS, and the home buttons of some Apple hardware.”
So, that claims Apple uses n = 5. However, https://applypixels.com/blog/the-hunt-for-the-squircle seems to indicate that’s close to, but may not be the exact shape of iOS icons (They’re approximating that curve with quadratic or cubic splines. That may be the sole cause of discrepancies)
Of course, they may use different values of n elsewhere.
