Can I watch national TV news broadcasts live, on Apple TV?

I haven't used any of the following, but this may help:

https://apps.nbcnews.com/tv/

https://www.cbsnews.com/news/cbs-news-launches-new-apple-tv-app/

https://abc.com/apps

https://apps.apple.com/us/app/cnn-breaking-us-world-news/id331786748?platform=appleTV

National news in which country?

Most broadcast networks (and their news programs) require a TV provider plan. That is their business model, for the most part. For the US: ABC, NBC, CBS, etc. do have their own apps for Apple TV, but those apps may have limited functionality without TV provider credentials (sign-in). The situation may be different in other countries than the US.

Find apps in the Apple TV App Store - Apple Support

TV providers may have their own app for Apple TV, with all channels in-app available, including news channels.

Apps that let you sign in with your TV provider on your iPhone, iPad, or Apple TV - Apple Support

TV providers that let you sign in on your iPhone, iPad, or Apple TV - Apple Support

Use your pay TV or cable provider with Apple TV - Apple Support

If you do not have a cable or satellite plan for TV access, then consider subscribing to one of the internet streaming TV providers (Hulu Live, YouTube TV, Sling TV, DirecTV Stream, Philo TV, FuboTV). [Comparison]

CBS affiliate stations (with CBS News) are included with a Premium subscription plan for Paramount+. That may be a viable option for some users.