Not open source, but I use the Google TV chromecast in “apps only” mode.

Its very minimal but you still get a single picture of whatever show is being promoted that week. No other intrusive adds have been added {yet}.

It also breaks Google Keep & Google Drive in Firefox.

Did you read the article?

1. Epic is not trying to get their 3rd party app in apples app store.
2. Epic can’t create a 3rd party app store because Apple revoked their developer license. This means any app epic creates can’t be sideloaded because it will never be signed by apple.
3. Apples new rules require any 3rd party app store to pay apple $0.50 per install (there is no million app install requirement for 3rd party app stores). So apple would still make money off epics app store if they allowed it.