library(shiny)
library(bslib)

ui <- page_navbar(
  id = "test",
  title = "Test Insert Navs",
  header = tagList(
    htmltools::tags$script(
      "Shiny.addCustomMessageHandler('active_nav', function(data) {",
      "alert(data.value);",
      "});",
    )
  ),
  nav(
    "Nav 0"
  )
)

server <- function(input, output,session) {
  
  nav_insert(id = "test", nav = nav(
    "Nav 1"
  ), select = FALSE)
  
  nav_insert(id = "test", nav = nav(
    "Nav 2"
  ), select = FALSE)
  
  observeEvent(input$test,{
    
    session$sendCustomMessage(
      type = "active_nav",
      message = list(value = input$test)
    )
  })
}

shinyApp(ui = ui, server = server)

R version 4.2.3 (2023-03-15 ucrt)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19045)

Matrix products: default

locale:
[1] LC_COLLATE=Spanish_Colombia.utf8  LC_CTYPE=Spanish_Colombia.utf8   
[3] LC_MONETARY=Spanish_Colombia.utf8 LC_NUMERIC=C                     
[5] LC_TIME=Spanish_Colombia.utf8    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] bslib_0.4.2 shiny_1.7.4

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.10          jquerylib_0.1.4      compiler_4.2.3       later_1.3.0         
 [5] shinyjs_2.1.0        tools_4.2.3          odbc_1.3.4           digest_0.6.31       
 [9] bit_4.0.5            memoise_2.0.1        jsonlite_1.8.4       lifecycle_1.0.3     
[13] lattice_0.21-8       pkgconfig_2.0.3      rlang_1.1.0          DBI_1.1.3           
[17] cli_3.6.1            rstudioapi_0.14      fastmap_1.1.1        withr_2.5.0         
[21] fs_1.6.1             vctrs_0.6.1          htmlwidgets_1.6.2    sass_0.4.5          
[25] hms_1.1.3            bit64_4.0.5          grid_4.2.3           fontawesome_0.5.0   
[29] R6_2.5.1             pool_1.0.1           blob_1.2.4           magrittr_2.0.3      
[33] promises_1.2.0.1     htmltools_0.5.5      ellipsis_0.3.2       rsconnect_0.8.29    
[37] mime_0.12            xtable_1.8-4         httpuv_1.6.9         shinybusy_0.3.1.9000
[41] cachem_1.0.7         zoo_1.8-12