On Facebook, you can ‘like’ a photo by pressing the ‘l’ key. I don’t know of any similar shortcut on YouTube; would it be possible to create an action to locate the ‘like’ button and click it? It will be at a different location on the screen depending on window size and location, as well as the page zoom and player view...
Unfortunately, YouTube does not have a keyboard shortcut for liking a video. You can see the list of keyboard shortcuts available at https://support.google.com/youtube/answer/7631406?hl=en
I am aware; my idea was something along the lines of creating an action to 'like' a video, either by moving the mouse to the thumbs up button, clicking it and returning the mouse to the prior position, or something like this....