Visit https://www.youtube.com/feed/channels and use the F12 Console tab to run this script

Unsubscribe from all YouTube channels

var i = 0;

var myVar = setInterval(myTimer, 3000);

function myTimer () {

    var els = document.getElementById("grid-container").getElementsByClassName("ytd-expanded-shelf-contents-renderer");

    if (i < els.length) {

        els[i].querySelector("[aria-label^='Unsubscribe from']").click();

        setTimeout(function () {

            var unSubBtn =  document.querySelector("[aria-label='Unsubscribe']");
            console.dir(unSubBtn.outerHtml);
            unSubBtn.click();

        }, 600);

        setTimeout(function () {

            els[i].parentNode.removeChild(els[i]);

        }, 1200);

    }

    i++;

    console.log(i + " Channels Unsubscribed\n");

    console.log(els.length + " remaining");

}