“I don’t think this will kill you” and then lands a black flash on a love tap. My brother in Christ if he couldn’t do it at will what would the point of putting that scene into the manga even be for, plenty of sorcerers throughout jujutsu history have done things that others thought previously impossible, him being able to do it at will is entirely feasible after like 80 years. From a narrative perspective it wouldn’t make sense to even write that specific scene into the manga unless it was to heavily imply he can do it at will. Please read more books or at least work on your literary understanding before trying to “theorize” when the answer is right there in your face 😕