When using the font modifier, set a weight to the font you’re passing.
For example, if you want to use one of the default text styles (which I recommend, since they adapt to the user’s Dynamic Type setting), you can do it like this:
Image(systemName: "arrow.right")
.font(Font.title.weight(.ultraLight))
If you want to specify a font size, you can do it like this:
Image(systemName: "arrow.right")
.font(Font.system(size: 60, weight: .ultraLight))