ZStack alignment not centered when in GeometryReader?

I have the following view:

struct TestView: View {
    
    var body: some View {
        GeometryReader { geo in
            ZStack(alignment: Alignment(horizontal: .center, vertical: .center)) {
                                
                    Text("TEST TEXT")
                
            }.background(Color.red)
        }
    }
    
}

Renders this:

I want views in the ZStack to be centered, and that only works if I remove the GeometryReader, like so:

struct TestView: View {
    
    var body: some View {
        ZStack(alignment: Alignment(horizontal: .center, vertical: .center)) {
            
            Text("TEST TEXT")
            
        }.background(Color.red)
    }
    
}

Renders this:

How can I use the GeometryReader and still have content in the ZStack be centered like shown in the last render picture above? Why is GeometryReader messing with the ZStack content alignment?

GeometryReader's alignment keeps changing - see GeometryReader Discrepancies with Previous OS Versions. To get the normal behavior, I usually just add .frame(maxWidth: .infinity, maxHeight: .infinity).

struct TestView: View {
    var body: some View {
        GeometryReader { geo in
            ZStack { /// no need for the custom Alignment
                Text("TEST TEXT")
            }
            .background(Color.red)
            .frame(maxWidth: .infinity, maxHeight: .infinity) /// here!
        }
    }
}

Result: