kableExtra in rmarkdown (pdf-output) with shiny app: ! Undefined control sequence

I have followed this issue in order to render a rmarkdown to pdf while using kableextra, but It fails when I'm using the shiny app. If I use the Knit button from Rstudio IDE, it will compile, but not from the shiny app !
I have prepared a minimal example as well :

library(shiny)
library(dplyr)
library(kableExtra)

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      numericInput("n_rows", label = "Number of rows to display", value = 10),
      downloadButton('report',"Generate Report")
    ),
    mainPanel(
      tableOutput("mtcars_table")
    )
  )
)


server <- function(input, output,session) {
  output$mtcars_table <- renderTable({
    head(mtcars, n = input$n_rows)
  })
  
  output$report <- downloadHandler(
    # For PDF output, change this to "report.pdf"
    filename = "report.pdf",
    content = function(file) {
      withProgress(message = 'Calculation in progress',{
        incProgress(session = session)
        tempReport <- file.path(tempdir(), "report.Rmd")
        file.copy("report.Rmd", tempReport, overwrite = TRUE)
        
        params <- list(df = mtcars[input$n_rows,])
        
        rmarkdown::render(tempReport, output_file = file,
                          params = params,
                          envir = new.env(parent = globalenv())
        )
        incProgress(session=session)
      }, session = session)
    }
  )
}


shinyApp(ui, server)  

And the report.rmd :

---
output:
  pdf_document:
    toc: false
    keep_tex: true
    number_sections: true
  documentclass: scrartcl
params:
  df: NA
header-includes:
  \usepackage[]{graphicx}
  \usepackage[]{xcolor}
  \usepackage{helvet}
  \renewcommand{\familydefault}{\sfdefault}
  \usepackage[T1]{fontenc}
  \geometry{verbose,tmargin=4.2cm,bmargin=2.5cm,lmargin=2.5cm,rmargin=2cm,headheight=1.6cm,headsep=1.2cm,footskip=1cm}
  \pagestyle{fancy}
  \setlength{\parskip}{\medskipamount}
  \setlength{\parindent}{0pt}
  \usepackage{textcomp}
  \usepackage{babel}
  \usepackage{pdflscape}
  \usepackage{tabularx}
  \usepackage{color}
  \usepackage{array}
  \usepackage{hyperref}
  \usepackage{ifthen}
  \usepackage{float}
  \usepackage{fancyhdr}
  \usepackage{framed}
  \usepackage{alltt}
  \usepackage{booktabs}
  \usepackage{makecell}
  \usepackage{longtable}
  \usepackage{multirow}
  \usepackage{wrapfig}
  \usepackage{colortbl}
  \usepackage{tabu}
  \usepackage{threeparttable}
  \usepackage{threeparttablex}
  \usepackage[normalem]{ulem}
  \usepackage{xcolor}
---

# Chapter title

```{r  echo=FALSE, message=FALSE, warning=FALSE,fig.pos = 'H'}
library(kableExtra)
df = params$df
kbl(df, booktabs = T, linesep = "") %>%
kable_styling(latex_options = "striped", stripe_index = c(1,2, 5:6))

Section title

\lipsum[1-10]

Start with the provided shinyApp code and report.Rmd, then compare PDF rendering through the RStudio Knit button with rendering through the shiny downloadHandler. Inspect the Undefined control sequence output and the generated LaTeX around the kableExtra table. Done means the same report renders successfully as a PDF from the shiny app.