Its more an issue I think of difficulty spike. I beat every other character first try, without issue. But suddenly, this final character introduces a new mechanic that isn't fun and additionally has lofty expectations of players. That some people managed to beat it once (can they do so reliably?) does not change that the difficulty spike feels like a difficulty cliff, and is far too great. I would still say the same thing had I managed to beat her. An easy mode I was not aware of, and I will circle back and try it when I have time. Though I still advocate that if you can't beat your own game, it needs rebalanced. I do love it, and without the fakeouts I feel the difficulty would go back in line with the rest of the characters and have a natural progression. That way it doesn't go from training you to "hit it as fast as you can", to "hit it fast but also don't, but also do" so suddenly. That some people have beaten it, or the existence of an easy mode, does not warrant or justify its difficulty.
But don't get my detailed critique wrong, it is an amazing game concept and its going to go far. I do really enjoy it, and want to see it shine bright as it can. As somebody who is disabled (mute) I very very much love getting to see or play a mute character. The art is immaculate too! Sound design superb! I do believe that the boss is the only thing hurting the game right now, and deeply at that. My main suggestion is, if not remove the fakeouts, is to make the fakeouts come in a predictable pattern. Every 3 shots for example.
If you do want to make adjustments, as per jam rules "You should only make tweaks and bugfixes for problems that heavily impact your game's performance or playability" you can adjust the boss if you desire. As "heavily impacts your playability" is an understatement, and people have made adjustments for less.
(edit: Oh and I know that there is the draw mechanic, but on doki sometimes even though it is red, the sound played, and I reacted in time, the game tells me "whoops you fired early that's a strike!" and I am pretty sure that is a bug)