chrome extension content script not working when url change but only works after refresh

Question

I'm developing a chrome extension to make some changes on Github site while the URL postfix matches the source code type (for example, xxx.cpp)

I expect the content.js will run every time the tab finishes loading the DOM elements. However, it only runs when I press the refresh button. If I click the hyperlinks and go to another URL, content.js won't run.

What did I do wrong? Thanks.

Following are the code.

manifest.json

{
    "name": "My Chrome Ext",
    "description": "change appearance of source code on Github",
    "version": "0.1",
    "manifest_version": 3,
    "permissions": ["storage", "activeTab"],
    "action": {},
    "content_scripts": [
        {
            "matches": ["*://github.com/*cpp"],
            "all_frames": true,
            "js": ["content.js"],
            "run_at": "document_end"
        }
    ]
}

content.js

window.alert("start running content.js");