Is there any option in WhatsApp that restricts posting messages by admin only? Others should not able post, but they should able to read the post.
Such a feature might soon be introduced, under the name of Restricted Groups:
The Restricted Groups setting can only be enabled by group admins.
Switching it on disables all chat functionality for non-admins – they won’t be able to send text messages, images, videos, GIFs, documents or voice messages, or share their location.
Admins, meanwhile, will be able to continue chatting as normal. Everyone else will simply have to read their messages in silence.
If a non-admin really wants to get a word in, they can do so by using the Message Admin button.
However, the message will need to be approved by the admin before going through to the rest of the group.