Just switched to the new Teams and encountered this issue.
Our use case is that there is a team with a "General" channel where a daily post is made from a manager/executive containing a distinct get-to-know-you type of question. Then all team members reply to that post with a status update on their tasks and a response to the question. I want to receive notifications that a post has been made in that channel, but I don't want to be dinged with a notification every time somebody else in the organization comments a reply to that post (unless they specifically @mention me).
Even if you globally disable the channel notifications to include only mentions, it only hides the "reply" notifications up until you decide to reply as well, after which you then receive all "reply" notifications after that. Previously, if you toggled on the "Disable notifications for this post" after replying yourself, then you stopped receiving the subsequent "reply" notifications. That option is now unavailable.