I have been having an issue with the TED app on my Apple TV 4K when Parental Controls are turned on although other apps (Netflix, Prime Video etc all work fine).
I have tracked this down to a repeatable error specific to the Pornography setting in Parental Controls. Turn it on and TED app does not work. Turn it off and all works fine.
Following further investigation I have also found a different workaround in that if I change the Apple TV DNS Server from Automatic to Manual and use the Google DNS Server 188.8.131.52 and switch ON Parental Controls all works again.
Parental Controls seems to be tricky and of course we would all like to be able to keep it switched on so hopefully this may help.