R shiny automatic download file to local after running a block of code

I have build a shiny app for non-technical user in my organisation to run script for standard task. The run time of script is around 30 mins or so. As I don't expect user to check the progress regularly, I am hoping to trigger download automatically after finishing running script, using the on.exit() function.

#pseudo example
library(shiny)

ui <- fluidPage(
   runButton = actionButton(
   inputId = "RunFunction1",
   label = strong("Run Function!"),
   color = "primary"))

server <- function(input,output) {
  observeEvent(input$RunFunction1,{
  
  #This is the main script i am running, which takes 30 mins. The function will save a large xlsx 
  #file in the working directory 
  standard_script

  # I am hoping to trigger the download on exit. However I am not sure how to point to the working 
  # directory
  on.exit(download.file())
  }
}

shinyApp(ui = ui, server = server)

I am aware that there is shinyjs solution out there. However, I would like to explore the on.exit download file option.