It’s more language dependent than ide. Go for instance makes unused variables a compiler error (I believe) which means ides mark it as red immediately.

Ts/js can have eslint rules against unused variables but they will still usually compile or just run directly anyway.

Java doesnt error but can be set to warn you on them.

Abap doesn’t care and won’t tell you.

Your mileage will vary.

I've seen it with multiple IDE's