Seems the broadcast feature will work very similarly to Telegram's broadcast channels in that an unlimited number of users can subscribe, but communication is broadcast one-way without any replies or comments from subscribers.
This is very useful for especially government, disaster management, news services, etc where millions of users can potentially tune-in, unlike with groups. Broadcast channels are also easier to manage as there is no moderation required.
But the differences come in with WhatsApp wanting to monetise these channels, and also limit them so that individuals are not able to use them. On Telegram's side, they have always been free, and even individuals could just create one and get going with them.
So WhatsApp continues to try keeping up with Telegram, but they always seem to be two steps or more behind with so many features. Yet we do know that the best features, the best security (I'm speaking broader than Telegram), most interoperable protocols, have never featured in the mass users' choice of what they use (just think VHS vs Betamax).
If corporates want to ever escape the ongoing squeeze of money out of them, they need to think open networks, interoperability, etc.
See WhatsApp launches Channels feature for broadcast messages
With Channels on WhatsApp, Meta is empowering its 2 billion users with more ways to stay connected and scrambling for monetization avenues.