He only had one hand when he killed Gojo.
this goes to show you don’t actually read.
A: Check back when he was in front of Gojo again, when they literally show he only had one hand.
B: Read this week's chapter, when they literally tell he only had one hand.
Sukuna made a binding vow to be able to kill Gojo despite only having one hand and not being able to use the technique. The binding vow made it so from then on he has to "make the signs and aim with his palm" (like he did against Kashimo). He has that extra condition now, as per the binding vow.
Going on a bit more on the topic.
The technique has two conditions:
Condition A: Make the hand signs.
Condition B: Aim with his palm.
We also know this:
- The technique now has extra requirements because of his binding vow.
- He couldn't use the technique with only one hand even before the requirements.
The technique already had Condition A before he used it on Gojo, and Condition B is new, as payment for skipping condition A that one time, which he skipped because he only had one hand remaining.
Two hands to make the MS hand sign, one hand to aim the slash. Three hands.