Shiny.fluent Stack function error


Following this shiny.fluent tutorial from 2 years ago

shiny.fluent live coding

and when I change the div to Stack, it throws an object error.

ui <- fluentPage(
  div(class = "ms-depth-4", tokens = list(padding = 20, childrenGap = 10),
    title = "Filters", 
    Toggle.shinyInput("includeOpen", label= "Include open deals", defaultChecked =TRUE)
  div(class = "ms-depth-4",
    Text("Sales Deals Details", variant = "xLarge"),

Can't find anything relating to this but is this Stack function maybe deprecated? What could I use instead for formatting?

I got it working by changing the ui/ server approach from straight:

ui <- fluentPage()
server <- function(input, output, session) {}
shinyApp(ui, server)

to the following which I've seen but not sure how it works or why necessary...

ui <- function(id) {
  ns <- NS(id)
  Card(title = "Filters", 
       Toggle.shinyInput("includeOpen", label= "Include open deals", defaultChecked =TRUE)

server <- function(id) {
  moduleServer(id, function(input, output, session) {}

if (interactive()) {
  shinyApp(ui("app"), function(input, output) server("app"))

Anyone know what is happening here? It also only shows when I open browser not the RStudio render window, is that as expected with this?