Good day.

I can't understand why the name is not transferred to the "DropDown Header"?

import SwiftUI

let actionButtonTest = ModelActionButton()
private var width: CGFloat = 200
private var height: CGFloat = 40
private var paddingV: CGFloat = 10
private var paddingH: CGFloat = 10
private var radius: CGFloat = 10.0
private var shadowRadius: CGFloat = 0
private var shadowX: CGFloat = 0
private var shadowY: CGFloat = 0
private var shadow: Color = .black
private var backColor: Color = .gray
private var forColor: Color = .white

struct DropDownAction {
    var title: String
    var action: () -> ()
}

struct DropDownButton: View {
    var actionModel: DropDownAction
    var select: (DropDownAction) -> ()

    var body: some View {
        Button(actionModel.title.uppercased(), action: {
                self.select(self.actionModel)
        })
    }
}

struct DropMenu: View {
    var menuActions: [DropDownAction]
    var select: (DropDownAction) -> ()

    var body: some View {
        VStack(spacing: 10) {
            ForEach(menuActions, id: \.title) {
                DropDownButton(actionModel: $0, select: self.select)
                    .frame(width: width, height: height, alignment: .leading)
            }
        }
        .parametrsButtom()
    }
}

struct DropDownHeader: View {
    @State var select: DropDownAction
    var action: () -> ()
    var expand: Bool

    var body: some View {
        Button(action: action) {
            HStack {
                Text(select.title.uppercased())     //  ???????    What transfer @select?
                Spacer()
                Image(systemName: "chevron.\(expand ? "up" : "down")")
                Text("\(select.title)")
            }
            .frame(width: width, height: height, alignment: .leading)
        }
        .parametrsButtom()
    }
}

struct DropDownView: View {
    var menuActions: [DropDownAction]
    @State var expand = false
    @Binding var select: DropDownAction

    var body: some View {
        VStack(alignment: .center, spacing: 0) {
            DropDownHeader(select: select, action: {
                expand.toggle()
            }, expand: expand)
            if expand {
                DropMenu(menuActions: menuActions) { action in
                    //action.action()
                    select = action
                    print(action)
                    print(select)
                    self.expand = false
                }
            }
        }
        .animation(.spring())
    }
}

struct DropDownView_Previews: PreviewProvider {
    //@State static var textTest: String = action.actionButton.first?.title ?? "Error"
    @State static var select: DropDownAction = action.actionButton.first!
    static var previews: some View {
        DropDownView(menuActions: actionButtonTest.actionButton, select: $select)
    }
}

struct ParametrsButtom: ViewModifier {
    func body(content: Content) -> some View {
        content
            .padding(.vertical, paddingV)
            .padding(.horizontal, paddingH)
            .foregroundColor(forColor)
            .background(backColor)
            .cornerRadius(radius)
            .shadow(color: shadow, radius: shadowRadius, x: shadowX, y: shadowY)
    }
}

extension View {
    func parametrsButtom() -> some View {
        self.modifier(ParametrsButtom())
    }

}

//---------

import SwiftUI

let action = ModelActionButton()

@main
struct DropButtonApp: App {
    @State var select: DropDownAction = action.actionButton.first!
    var body: some Scene {
        WindowGroup {
            DropDownView(menuActions: action.actionButton, select: $select)
        }
    }
}

//---------

import Foundation

class ModelActionButton {
    let actionButton: [DropDownAction] = [
        .init(title: "First", action: {} ),
        .init(title: "Second", action: {} ),
        .init(title: "Third", action: {} )
    ]
}

figured it out! confused @State and @Bindind places