I got a similar thing on my Roku. Unfortunately content from Disney+, CBS All Access and other third party apps that 'link' to the TV app on an ATV don't show up on the Roku's version of the app. Just Apple content. Last I checked, even ATV+ stuff didn't show up.
I just had to do another plug pull restart today, since CBS All Access crashed or something, I was browsing the list of series on that 'channel,' tried watching Brady Bunch, and was told to install Hulu or pay. Tried rebooting the unit, via the settings, but same issue. Pull the actual cord from the back, and plug it in, wait for it to do a full restart, and the show works.
I'm really getting tired of this. It just got another 'update' to tvOS 14.4, uncommanded (I got auto updates off, blocked at the router, and it didn't notify me one bit--just woke up to the 'what's new' screen.) That update had happened before my attempt to watch The Brady Bunch. I'm trying to figure out how to remove the Health app since I have no need for it on an Apple TV, and it's just annoying having a useless app sitting there. Also don't like the TV+ menu in the TV app, as it's redundant (right up there with ellipsis, gear and three-dot menus on apps these days).