A polyfill for script element loading (for illustration purposes)

script-parsing.js

function parseHTML(getNextElement) {
  let doneParsing = null;
  const whenDoneParsing = new Promise(resolve => { doneParsing = resolve; });

  while (const element = getNextElement()) {
    if (element.tagName !== "SCRIPT") {
      // parse everything else...
      continue;
    }

    const whenSourceLoaded = fetch(element.src).then(response => response.text());

    if (element.async) {
      whenSourceLoaded.then(eval);
    } else if (element.type === "module" || element.defer) {
      Promise.all([whenSourceLoaded, whenDoneParsing]).then(([source]) => eval(source));
    } else {
      eval(await whenSourceLoaded); 
    }
  }

  // This will execute all scripts that are already loaded in the same task
  doneParsing();
}

Do all module scripts actually run before all deferred (if they are loaded by the parse is complete)?

Do all module scripts actually run before all deferred (if they are loaded by the parse is complete)?

Yes! Though I think it's a Chromium thing rather than a standard thing
https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/script/html_parser_script_runner.cc;l=453?q=parser_script_R

OK

Do all module scripts actually run before all deferred (if they are loaded by the parse is complete)?

OK actually it was a mistake, was thrown off by "force deferred" script which is a non-standard chromium feature.