SvelteKit wait for Firebase onAuthStateChanged before load function

I’m working with SvelteKit and Firebase to build a website. There’s a document in my Firestore that only logged in users can accces, I already set a rule for that. The problem that I’m facing is that the load function which fetchs data from the database is sending back a permission denied error as if the user is not logged in. The load function seems to run before the auth state if changed.

I tried using a simple store that stores the authenticated user to check if the user is signed in, but unfortunately the getDoc function can’t be awaited

// $lib/stores/authStore.js
import { writable } from 'svelte/store';
import { auth } from '$lib/firebase';
import { onAuthStateChanged } from 'firebase/auth';
export function authStore(auth) {
    let unsubscribe;

    const { subscribe } = writable(auth.currentUser, (set) => {
        unsubscribe = onAuthStateChanged(auth, (user) => {
            set(user);
    });
    return () => unsubscribe;
    });

    return {
    subscribe
    };
}

// +page.server.js
import { authStore } from '$lib/stores/authStore.js';
import { doc, getDoc } from 'firebase/firestore';

export async function load() {
    let protectedDoc;
    authStore.subscribe((user) => {
        if (user) {
            const docRef = doc(db, 'myCollection/myDoc')
        await getDoc(docRef).then((snapshot) => {
                protectedDoc = snapshot.data();
            });
            return { protectedDoc }
        };
    })
}

I tried something similar to a few discussions, but had no success
SvelteKit async function load not working or Firebase onAuthStateChanged cannot be made blocking

Firebase split second authentication confirmation is messing with Sveltekit pages due to Firestore rules

Sveltekit: Wait for resolve in +layout.ts before load() in +page.ts

How should I write this load function in order to the read the firebase document only after user auth state is not null?