just run code in console by one click

unsub_all_youtube_channel.js

(function(){
    var btns = document.getElementsByTagName('button');
    for (var i = 0; i < btns.length; i++) {
        if (btns[i].dataset.isSubscribed == "True") {
            if (!!btns[i].dataset.showUnsubConfirmDialog) {
                delete btns[i].dataset.showUnsubConfirmDialog;
            }
            btns[i].click();
        }
    }
})();