R Shiny - How to do multiple tasks at the same time in one session? Such as two calculations or two timer

How can R(Shiny) perform multiple tasks at the same time? For example have a "clock" or timer in your UI which keeps on ticking while having an another "ObserveEvent" trigger/calculation running?

See the following example in Shiny below. When you press "click", the clock freezes since R starts focussing on the for loop.

ui <- fluidPage(
  h2(textOutput("currentTime")),
  actionButton("click","click")
)

server <- function(input, output, session) {
  output$currentTime <- renderText({
    invalidateLater(1000, session)
    paste("The current time is", Sys.time())
  })
  
  observeEvent(input$click,{
    showNotification("Computation started!", type = "error")
    #Sys.sleep(2)
    for(i in 1:(8*10^7)) 1 + 1
    showNotification("Computation finished!", type = "error")
    
  })
  
}

# Create Shiny app ----
shinyApp(ui, server)