IOSCO has no power to make law anywhere. What it does is agree principles on matters such as market abuse, benchmark integrity, conduct standards for intermediaries, and crypto-asset supervision, which member regulators then implement through their own rulebooks.
Its multilateral memorandum of understanding matters more day to day. Signatory regulators use it to obtain bank records, trading records, and witness statements from each other, which is how an offshore account trading on inside information in a US stock still gets traced.
When you see similar rules appearing in the UK, EU, Singapore and Australia within a few years of each other, an IOSCO principle is often the common ancestor.
Related: sec, fca, esma, mas-singapore, insider-trading