ipywidgets FileUpload does not work when using Voila

Question

I'm trying to upload an image through the ipywidget FileUpload widget:

btn_upload = widgets.FileUpload()

To be able to run inside a notebook, I had to adjust websocket_max_message_size, otherwise, the notebook hangs, as reported here.

I could do that using classical jupyter server using a customized jupyter_notebook_config.py

jupyter notebook --config="/path/to/user/.jupyter/jupyter_notebook_config.py" bear_classifier.ipynb

...
c.ServerApp.tornado_settings = {"websocket_max_message_size": 100 * 1024 * 1024}
...

When running the notebook, I'm unable to adjust this websockect_max_message_size, so the execution hangs after selecting a file.

I already tried setting config through command line options

voila bear_classifier.ipynb --Voila.tornado_settings="{'websocket_max_message_size': 209715200}"

Or even through a custom app

from voila.app import Voila, _, Dict

class CustomVoila(Voila):
  tornado_settings = Dict(
    {
      'websocket_max_message_size': 209715200
    },
    config=True,
    help=_(
        "Extra settings to apply to tornado application, e.g. headers, ssl, etc"
    ),
  )

app = CustomVoila()

Do you have any idea what else could I try?