I’m on a Mac, but since Adobe took away the nifty way to insert keyframe markers, I’ve lamented the movement needed to do this.
I found a way to do it. Set up your keyboard preferences in “tools” for “pen-tool” to something simple like “q” – (the regular grabber is “v” so you can always go back.
Then – as you work – hit “q” (now your cursor is pen-tool, and place you mouse where you want the keyframe. Hold down the Mac-key (try something else on PC) and you can now click to make a keyframe marker on the timeline.