A script that can be executed to unsubscribe all the YouTube channels at once.

unsubscribe-youtube-channels.js

var i = 0;
var count = document.querySelectorAll(
  "ytd-channel-renderer:not(.ytd-item-section-renderer)"
);
myTimer();
function myTimer() {
  if (count == 0) return;
  el = document.querySelector(".ytd-subscribe-button-renderer");
  el.click();
  setTimeout(function () {
    var unSubBtn = document.getElementById("confirm-button").click();
    i++;
    count--;
    console.log("channel " + i + " unsubscribed");
    setTimeout(function () {
      el = document.querySelector("ytd-channel-renderer");
      el.parentNode.removeChild(el);
      myTimer();
    }, 250);
  }, 250);
}

This one is working. First, you have to go to the bottom of the page and then open up the console.

This ran through everything said i was unsubscribed took about 20 min for 600 subs. Said it was successful but back in YouTube they are all still showing as subscribed. I have tried logging out and in and clear cache but all still showing not 1 removed????