>I can see If can make it an option, I assume hitstop on hit is fine?
The hitstop is fine. I saw you mentioned Hollow Knight as an inspiration, and I thought it was pretty jarring there as well. Maybe add some kind of effect to highlight the player and whatever hit you during the hitstop.
>I had another atk for the shield boss itself(cutted for reasons*), and I guess the boss is the problem? For example adding more type of Options that follow the boss won't solve the issue for you? Another example, if the boss had less life (so you would play phase one just two times) it would be better? My philosophy so far is to have quick but deadly boss encounters, like contra, not marathons like ddp and some touhou.
It's more that the second phase is just a lot more engaging. It can't really hurt you in phase 1 and you're mostly just flying in circles to get it to stop blocking your shots instead of dodging attacks.
I also noticed that boss projectiles don't despawn when the boss dies. Make them do that so you can't die after a boss is already dead.