Grow from bottom of shape instead of centre?

[Gnielio]

Grow from bottom of shape instead of centre?

[Asperi-Demo]

(please next time give a link to which file you refer)
Well, in your code there is no fixed bottom (as an anchor point), so rectangle grows in both direction, because by-default alignment is center. To make it grows in some direction you have to specify some fixed area and give inside content alignment to bottom, then any growth in it from 0 will be to top (to fill area), like

   // this is different stack
   ZStack(alignment: .bottom) {      // content will be aligned to bottom
            Text("Hola")
                .foregroundColor(.black)
                .font(.headline)
            RoundedRectangle(cornerRadius: 5)
                .frame(width: 100, height: height, alignment: .center)
                .foregroundColor(Color("RedColour"))
                .onShake {
                    withAnimation {
                        height = 100      // << here !!
                    }
                }
   }.frame(height: 100)    // fixed area, so shape is initially at bottom and will grow upward