crx-page-title

background.js

const title = "Inactive Tab";

function changeDocumentTitle(documentTitle) {
    document.title = documentTitle;
}

chrome.tabs.query({ active: false }, tabs => {
    tabs.forEach(tab => {
        if (!tab.url.startsWith('chrome://')) {
            chrome.scripting.executeScript({
                target: { tabId: tab.id },
                func: changeDocumentTitle,
                args: [title]
            });   
        }
    });
});

manifest.json

{
    "name": "Page Title Changer",
    "description": "Changes Title of All Inactive Tabs",
    "version": "1.0",
    "manifest_version": 3,
    "background": {
        "service_worker": "background.js"
    },
    "permissions": [
        "scripting",
        "tabs"
    ],
    "host_permissions": [
        "<all_urls>"
    ]
}