An easier way to make a button style with closure or passing an instance of ViewModifier.

Button("Button") {
  print("")
}
.buttonStyle(
  ButtonStyleModifier { label, state in
    label
      .padding()
      .background(
        RoundedRectangle(cornerRadius: .infinity, style: .continuous)                
          .foregroundColor(Color.secondary)
      )
      .opacity(state.isEnabled ? 1 : 0.3)
}

ButtonStyleModifier supports indicating state of processing by .processing() modifier.
This state can be read from state parameter in ButtonStyleModifier.

ButtonStyleModifier sets the following environment values for making styles in ViewModifier.

extension EnvironmentValues {
  @Entry public var _styled_isPressed: Bool = false

  @Entry public var _styled_isProcessing: Bool = false
}