Use of the global busy indicator

shiny
1

How does the global busy indicator introduced in Shiny 1.9 work?
I thought it should appear in the first 5 seconds in the following example:

library(bslib)

ui <- page_fillable(
  useBusyIndicators(),
  card(
    card_header(
      "A plot",
      input_task_button("simulate", "Simulate"),
      class = "d-flex justify-content-between align-items-center"
    ),
    plotOutput("p")
  )
)

server <- function(input, output) {
  Sys.sleep(5)
  
  output$p <- renderPlot({
    if(input$simulate > 0){
      Sys.sleep(4)
      plot(x = rnorm(100), y = rnorm(100))
    }
  })
}

shinyApp(ui, server)