I had a ton of trouble getting the knife tool to do anything. I seemed to have missed the mirror application at first so I took care of that and still had issues. After a bit of frustration, it turns out I had to merge duplicates on the entire object before the knife tool would act like it does in the video.
Aside from applying modifiers I need to add merge duplicates and apply scale to my muscle memory.
Here’s to hoping this message finds someone with similar troubles.