I encountered the same issue. Take a look at the function signature:

export declare function toSignal<T>(source: Observable<T> | Subscribable<T>): Signal<T | undefined>;

If you want to specify an initialValue, you need to avoid explicitly adding the generic type like . Instead, write it as follows:

this.scrollLimit = toSignal(this.scrollDispatcher.scrolled(), { initialValue: true });

By removing , TypeScript can correctly infer the type, and the initialValue option becomes functional.

Regards