I would recommend trying out https://github.com/jimmywarting/native-file-system-adapter
it have a self hosting service worker solution that don't involve iframes and 3rd party iframes

On my project (https://webscan.goncalomb.com/) that uses SharedArrayBuffer / COEP, I'm using a document.createElement proxy to add the credentialless attribute that allows the iframe to load. I've opened a pull request, #329. Meanwhile you can use this snippet (it affects all iframes created with document.createElement):

const documentCE = document.createElement;
document.createElement = (...args: Parameters<Document['createElement']>) => {
  const el = documentCE.apply(document, args);
  if (args[0] === 'iframe') {
    el.setAttribute('credentialless', '');
  }
  return el;
};

https://developer.chrome.com/blog/iframe-credentialless/

https://developer.mozilla.org/en-US/docs/Web/Security/IFrame_credentialless