All apps on smart TVs are browser apps. Some, like Youtube, get special privileges (that is, can run their own app), but also need to run some kind of UI since TVs have no standard UI libraries. Youtube decided to run a stripped down version of Chrome (Cobalt). Others (IIRC Netflix) run their own renderer. Or do weird stuff, see Comcast and Lightning https://www.lightningjs.io/

TVs own interfaces are some bespoke one-off stuff that isn't exposed to other apps.

And this sucks because Raspberry PIs have more powerful hardware than even modern high-end TVs.