One way to do it is with @genType.as:
// Libname.res
@genType.as("libname")
let make = ...
@genType.as("useLibname")
let use = ...
Bear in mind that that @genType.as feature is deprecated because in the future (V12?) we want genType to not create any runtime code.
But you would probably keep some entrypoint index.js/ts file anyway, where you could just re-export what the user should consume (ReScript won’t look into your index.js).
Other than that I think @DZakh knows more about publishing for both langs.
EDIT: I also found this post which might be useful: Distribute npm package for non-ReScript users - #10 by DZakh