Update your bookmarklet.
TLDR use this new one now.
javascript:eval(atob('c2V0SW50ZXJ2YWwoZnVuY3Rpb24gKCkgewogIGZvciAoZSBvZiBbCiAgICAuLi5kb2N1bWVudC5nZXRFbGVtZW50c0J5Q2xhc3NOYW1lKCd5dHAtc2tpcC1hZC1idXR0b24nKSwKICAgIC4uLmRvY3VtZW50LmdldEVsZW1lbnRzQnlDbGFzc05hbWUoJ3l0cC1hZC1za2lwLWJ1dHRvbi1tb2Rlcm4geXRwLWJ1dHRvbicpLAogICAgLi4uZG9jdW1lbnQuZ2V0RWxlbWVudHNCeUNsYXNzTmFtZSgneXRwLWFkLXNraXAtYnV0dG9uIHl0cC1idXR0b24nKSwKICBdKSB7IGUuY2xpY2soKTsgfQp9LCAxMDAwKQ=='))
Here is the decoded javascript
setInterval(function () {
for (e of [
...document.getElementsByClassName('ytp-skip-ad-button'),
...document.getElementsByClassName('ytp-ad-skip-button-modern ytp-button'),
...document.getElementsByClassName('ytp-ad-skip-button ytp-button'),
]) { e.click(); }
}, 1000)
It seems the skip ad button is now referred to as the ‘ytp-skip-ad-button’. Fun times.