Calisthenics Unity

Does one arm push up build strength to do handstand push-up

I think the one arm push up is harder than the hspu, but there is a carry over in strength gains. I think its better to progress with pike push ups with feet elevated and handstand holds to build the shoulder strength needed though

Does one arm push-up doesn't build shoulder strength for handstand pushup

It doesnt target the shoulders much, mainly the chest and tricep

Exactly. I would suggest pike push ups!