I’ve found that most of the various alloy cleaners out there are pretty much all Hydrofluoric acid based (some even come with a splash of Sulphuric acid thrown in for some extra zing).
When I was looking for something slightly less toxic to clean up my boat hull I stumbled across
Kleen-a-hull which is Phosphoric acid based and slightly less burn your face off toxic as the other options.
This stuff did a good job removing 10 years of stains off the tinny. Just diluted it as per the instructions and rinsed it off properly.
I would only go down this path if the alloy step is on its own and not connected to a steel frame (or vehicle).