Gists for the post - https://rizwaniqbal.com/posts/paginating-firestore-collections-with-snapshot-listeners/

snapshotWatchers.ts

private snapshotWatchers: Array<() => void> = [];
private syncRequest: Partial<ObservablePaginatedQuery>;

private syncCards() {
    
    // assume some code here to initialise variables, create a service instance et al

    // syncRequest is a class variable
    this.syncRequest = WatchPaginatedCards();
    this.syncRequest.cards.pipe().subscribe(
        t => {
            // do something with the cards received
        }
    );
}

// to get next page
public getNextPage() {
    const snap = this.syncRequest.nextPage.next();
    return snap.value !== undefined && this.snapshotWatchers.push(snap.value);
}

// to stop listening to changes to a particular page
this.snapshotWatcher[3]();

//or all
() => {
    for (const snapshot of this.snapshotWatchers) {
        snapshot();
    }
}