This keeps changing. I think Apple does not like people to pay directly to CBS.
Even though I have a CBS subscription through Apple subscription service on my iphone, and even though in Apple TV app, in settings, the app is connected to CBS app and it shows I have an active subscription, the Apple TV app does not let me watch CBS and says I need to get a 2nd subscription!!!!!!!
Things like these are why people are fleeing to other services.
iPhone XS Max
You can’t use the Apple TV app Channel CBS if you signed up for CBS outside the Apple TV app. These subscriptions are not exchangeable like that. Different licenses, different perks.
You can set a show to link correctly to the separate CBS app, by changing the content provider on the Information/Details page for that show (section: How to Watch).
Subscribe to Apple TV channels in the Apple TV app - Apple Support
However, if your subscribe to CBS through the Apple TV app, then CBS allows you to convert that to an additional true CBS account, to be able to watch it on the web and in the separate CBS app too. (More content providers should be so modern and flexible!)
CBS all access not active in Apple TV
