Posting to a channel will post to all accounts subscribed to that channel. There is no direct way to exclude an account from a channel post. If a user doesn't want to send content to a certain social account each time a post is added, the account shouldn't be subscribed to that channel.
If a user is looking for a more customized post, they should use the Share to My Account option under under Queue → Create Post.
If a user really wants to post from a channel and exclude a social account, they can select Create Posts for Channels under Queue → Create Post, fill in the content for the social accounts they'd like to post to, and leave the section blank that they do not want to post to. For example, if they leave Instagram blank, the post will fail for Instagram only.
If you have any questions, please reach out to our Success team at email@example.com.