Hi VananNavarasan
My name is Daniel. I will be more than happy to assist you.
As of today, only one channel has announcement posts as a native feature. If you don't want to post it on the channel, as an alternative, you can send it via private group chat.
Disclaimer:
This is a peer-to-peer support forum. I'm Non-Microsoft Staff, I don't work for Microsoft. Mostly everyone here are users, helping other users.
Kind Regards