Apple TV 3 vr 8.4.4
when I try to go on to add apps …
The Apple TV box (3rd generation) [A1427 or A1469] is from 2012, and doesn’t support user-added apps.
It was discontinued in 2016, and became ‘obsolete’ for support in 2022. What works may keep working, but if any service is changed in a way that makes it incompatible with this model, then that marks the end for that service on this model. Content providers may choose to not support this model anymore. This model is not expected to receive further software updates (last update 2022-03-14). Unsupported apps may be removed from the Home Screen automatically, as they load from Apple servers at startup.
Apple TV 4K, tvOS 16
The 4K models are modern, newer, and very different models [A1842, A2169, A2737, or A2843]. These models support user-added apps from an on-device App Store.
Identify your Apple TV model - Apple Support
Find your Apple TV model number - Apple Support