I guess you are still using JSX V3? Not sure if that is possible. @moondaddi maybe knows more.
Personally, I would use JSX V4 where that example compiles in uncurried mode: ReScript Playground
But actually, I would not use forwardRef at all, since it’s discouraged, even by the React team.
And in React 19 you will be able to just pass it as any other prop.