Loading data server side and allow global access client side

I'm having a hard time understanding the use of Runes and data loading.I load a supabase json file and I want to access the data globally.

// +page.server.jsexport async function load() {    const [_portfolioSummary, error] = await getFullPortfolio('/');    return _portfolioSummary;}

// shared.svelte.jsexport let portfolioSummary = $state({});

// +page.jsimport { portfolioSummary } from '../lib/js/shared.svelte.js';export async function load({ data }) {    portfolioSummary = data.portfolioSummary;}

I get this error:

TypeError: Cannot set property portfolioSummary of #<Object> which has only a getter

What should I do to get portfolioData globally so I can use it anywhere?