so, no hand signs = no world slash
guess i was wrong with this.
sukuna only had one arm when he used world slash against gojo. he couldn't use hand signs. so it's not the case.
what's matter is the hwb.
sukuna can use hwb and cleave/dismantle simultaneously.
but he can't simultaneously use hwb and world slash (narrator said that he released hwb to use it).
looks like one of conditions to use world slash is that it can't be used along with any other technique (barriers, domains, etc).
sukuna released hwb to cast world slash, but boys interrupted him.
the he enchants his output and finally uses world slash or just obliterates them with point blank dismantle, while there were close to him (kusakabe mentioned, that cleave and world slash are instakill, as well as point blank dismantle)