When the TypeScript compiler option exactOptionalPropertyTypes is enabled, RTK Query hook results don’t narrow data (and similarly error) after status flag checks. For example, inside an if (result.isSuccess) block, result.data still has the type T | undefined instead of narrowing to T. With the flag disabled, narrowing behaves as expected.

Reproduction
https://github.com/chirophobic/rtkquery-exact-optional-property-types-