Thanks for the post, @MarkusP!
We're sorry for the inconvenience. Try connecting it to a mobile hotspot and see if you can update your device.
If the issue persists, we would recommend communicating this with the TV manufacturer support team for further assistance. Each Roku TV manufacturer provides direct support and warranty services for their products running the Roku OS.
You can contact them here: TCL Support or at 1-877-300-8837.
Thanks,
Rey
ERey.
Roku Community Moderator