First of all, it is not a good idea to mix mutable state with fixed values like this. There is no reason for the options to exist in a writable store if they cannot change.

As for how to make this more convenient: You can store all values in a single object and serialize it as JSON.

The most basic example:

import { browser } from '$app/env';
import { readable, writable } from 'svelte/store';

function localStorageStore(key, initial) {
    if (browser == false)
        return readable(initial);

    const value = localStorage.getItem(key)
    const store = writable(value == null ? initial : JSON.parse(value));
    
    store.subscribe(v => localStorage.setItem(key, JSON.stringify(v)));
    
    return store;
}

const options = {
    speed: ['slow', 'medium', 'fast'],
    sound: ['on', 'off'],
    tiles: [4, 6, 8],
    theme: ['light', 'dark'],
}

const settings = localStorageStore('so.lss', {
    speed: 'slow',
    sound: 'on',
    tiles: 4,
    theme: 'light',
});

Since the localStorage access is encapsulated in a function anyway, you could also easily create a store for each option individually.

If you want a generic way to use options and settings together, you can just iterate via Object.entries, e.g.

{#each Object.entries(options) as [key, items]}
    <select bind:value={$settings[key]}>
        {#each items as item}
            <option value={item}>{item}</option>
        {/each}
    </select>
{/each}

Note: The store implementation is just for illustrative purposes. You would probably want a more complex mechanism that handles:

• Non primitive types, e.g. this will fail for Date objects, as they will not be parsed back to a Date.
• Versioning and migration of values. As soon as you want to change the format of a setting, you will have to deal with outdated values existing on user machines.
• The storage event, if the store should be synchronized across multiple tabs.

If you must keep that object format, you can also just re-map it into its components:

const configuration = {
    speed: {
        options: ['slow', 'medium', 'fast'],
        selected: 'slow'
    },
    sound: {
        options: ['on', 'off'],
        selected: 'on'
    },
    tiles: {
        options: [4, 6, 8],
        selected: 4
    },
    theme: {
        options: ['light', 'dark'],
        selected: 'light'
    },
};

const options = Object.fromEntries(
    Object.entries(configuration)
        .map(([key, value]) => [key, value.options])
);

const settings = localStorageStore(
    'so.lss',
    Object.fromEntries(
        Object.entries(configuration)
            .map(([key, value]) => [key, value.selected])
    )
);

options/settings will be equivalent to the first example.