How to add a subtitle below a large title in a navigation view in swift ui?

You could try something like this:

 NavigationView{
            VStack(){
                //"Some code"
            }
            .navigationBarTitleDisplayMode(.large)
            .toolbar {
                ToolbarItem(placement: .navigationBarLeading) {
                    VStack {
                        Text("Title").font(.largeTitle).bold()
                        Text("Subtitle").font(.subheadline)
                    }
                }
            }
        }

Seems "navigationSubtitle" is only for macos, this is another way to do it in ios:

        .navigationBarItems(leading: VStack {
            Text("Analytics").font(.largeTitle).bold()
            Text("Subtitle")
        })

Edit update:

you could also try this, with some loss of font choice:

.navigationTitle("Subtitle") 
.navigationBarItems(leading: Text("Analytics").font(.largeTitle).bold())

I have found a solution to what I was looking for: basically create the top of the screen as it would normally be without a navigationView and then add a scrollview underneath.

HStack {
    VStack(alignment: .leading, spacing: 5) {
        Text("Title")
             .font(.largeTitle)
             .foregroundColor(Color(UIColor.label))
             .fontWeight(.bold)
                        
        Text("subtitle")
             .font(.subheadline)
             .foregroundColor(Color(UIColor.label))
     }
                
     Spacer()         
 }
 .padding()
            
            
            
 ScrollView(.vertical, showsIndicators: false) {}