Comment by Hitton

Enhancer for YouTube can do that, but you can also do it with simple userscript. The userscript I found somewhere few years ago:

  // ==UserScript==
  // @name         Mediabord
  // @version      01.1
  // @description  tryd to take over the world!
  // @author       j
  // @match        *://*/*
  // @grant metadata
  // ==/UserScript==
  
  document.addEventListener('keydown', function(event) {
      var vidz = document.querySelectorAll('video');
      function is_text_box(element){
          var tagName = element.tagName.toLowerCase();
          return  tagName === "textarea" || tagName === "input";}
      if(is_text_box(event.target))
          return false;
      vidz.forEach(vidz => {
          switch (event.keyCode) {
              case 221: // (])
                  vidz.playbackRate+=0.25;
                  break;
              case 219: // ([)
                  vidz.playbackRate-=0.25;
                  break;
              case 220: // (\)
                  vidz.playbackRate = 1;
                  break;
              case 83:
                  vidz.currentTime+=3;
                  break;
              case 65:
                  vidz.currentTime-= 3;
                  break;
          }
  
      });
  });