tkinter not working in shinyapps.io

Hi,
has anyone ever successfully deployed a Shiny App that uses reticulate and python3-tk (tkinter) to shinyapps.io? I've tried multiple times and ways but it didn't work out yet.
My app creates a python-virtualenv and locally on my laptop, it works without installing pyton3-tk into the venv but on shinyapps.io it doesn't - the logs say I need to install it. But installing it works neither locally nor on the web page.

reticulate::virtualenv_create(envname = virtualenv_dir, python = python_path)
reticulate::virtualenv_install(virtualenv_dir, packages = *python3-tk here*, 
                                 ignore_installed=TRUE)
reticulate::use_virtualenv(virtualenv_dir, required = T)

I'm getting frustrated. Thanks a lot for your help.
Lea