library(targets)
library(tarchetypes)
tar_manifest(fields = all_of("command"))

shiny::shinyApp(
  ui = shiny::actionButton("run", "run"),
  server = function(input, output, session) {
    shiny::bindEvent(
      shiny::observe({
        targets::tar_destroy(ask = FALSE)
        targets::tar_make(names = "model", callr_function = NULL)
      }),
      input$run,
      ignoreInit = TRUE
    )
  }
)

✔ ended pipeline [51ms, 0 completed, 0 skipped]
Warning: Error in : Error in tar_make():
  attempt to apply non-function
  See https://books.ropensci.org/targets/debugging.html
  94: <Anonymous>
  93: signalCondition
  92: signal_abort
  91: rlang::abort
  90: tar_error
  89: tar_throw_run
  88: callr_error
  86: callr_outer
  85: targets::tar_make
  84: ::
shiny
observe [~/.active-rstudio-document#11]
  83: <observer>
   4: runApp
   3: print.shiny.appobj
   1: source