There is a float() function, similar to the int() function. These were (very recently) deprecated in favor of using the constructors (Int(), Float64(), etc.)
In 24.6, SIMD didn’t have a constructor that took a Floatable value, so you’d have to use float() or to_float64(). In the latest nightly, you should be able to do Float64(item) … If you’re on nightly and that’s not working for you, please open a bug.