Navigate tab to a URL and execute script inside

I am struggling to get this simple f-ty working... My scenario is:

1. get current URL
2. modify it
3. navigate/redirect to it
4. execute custom JS code there

The most problems I have is with 4)

manifest.json

{
  "name": "Hello, World!",
  "description": "Navigate and execute custom js script",
  "version": "1.0",
  "manifest_version": 3,
  "permissions": [
    "tabs",
    "activeTab",
    "scripting"
  ],
  "background": {
    "service_worker": "background.js"
  },
  "action": {}
}

background.js

function myCustomScript() {
    alert('myCustomScript test ok!');
    console.log('myCustomScript test ok!');
}

chrome.action.onClicked.addListener((tab) => {

    chrome.tabs.update({url: "https://example.com"}, myCustomScript);

});

The page got redirected but my js function is not executed! Do you know why and how to fix it?

P.S: this is my first time I am creating my chrome extension, maybe I am doing something wrong...

To execute custom code, use chrome.scripting API. For this scenario you'll need:

1. "scripting" added to "permissions", which you already have,
2. "https://example.com/" added to "host_permissions" in manifest.json.

Note that activeTab permission won't apply to the tab after it's navigated to a URL with a different origin because this permission only applies to the currently shown origin.

Due to a bug in Chrome, you need to wait for the URL to be set before executing the script.

chrome.action.onClicked.addListener(async tab => {
  await chrome.tabs.update(tab.id, {url: "https://example.com"});
  // Creating a tab needs the same workaround
  // tab = await chrome.tabs.create({url: "https://example.com"});
  await onTabUrlUpdated(tab.id);
  const results = await chrome.scripting.executeScript({
    target: {tabId: tab.id},
    files: ['content.js'],
  });
  // do something with results
});

function onTabUrlUpdated(tabId) {
  return new Promise((resolve, reject) => {
    const onUpdated = (id, info) => id === tabId && info.url && done(true);
    const onRemoved = id => id === tabId && done(false);
    chrome.tabs.onUpdated.addListener(onUpdated);
    chrome.tabs.onRemoved.addListener(onRemoved);
    function done(ok) {
      chrome.tabs.onUpdated.removeListener(onUpdated);
      chrome.tabs.onRemoved.removeListener(onRemoved);
      (ok ? resolve : reject)();
    }
  });
}

P.S. alert can't be used in a service worker. Instead, you should look at devtools console of the background script or use chrome.notifications API.