Status: refused by design
Number?.(x) is not FunctionalScript. Number?.(x) is valid JavaScript, and fjs compile refuses it by design: the demo below shows what it prints.
?.( calls a value unless it is null or undefined. A conversion is an operator, not a value, so it has no nullishness to guard, and Number?.(x) is refused at the word. The conversion is written Number(x).
The row op.guarded-conversion of refused constructs registers the refusal, and operators and functions gives its reason.
export default Number?.("1");
The demo on this page compiles sample.mjs, the module above, with this build's fjs compile, and shows the line it prints and the token it refuses. Below that it shows what JavaScript answers for the same module: 1.
Write the conversion without the guard, as alternative.f.js does:
export default Number("1");
It answers 1.
Today fjs compile prints reserved word at the refused token. The demo proposes what it should print instead: the reason at the same token, what JavaScript does there, and the allowed spelling, the line alternative.f.js writes, as help. The page compiles the alternative too, so the suggestion is one the compiler accepts.