Just FYI, if you're looking for the setting, it should be called "show iPhone reactions as emoji". I think it's enabled by default for all of those the feature has rolled out to.
As 9to5Google points out, there are inconsistencies between how reactions are represented on each operating system. [...] they could lead to significantly different interpretations of a reaction’s meaning.
I wonder if this is just a strategy to mess with Apple, and maybe also a response to the blue bubbles