As mentioned in the comments, the status and reasons for this change are discussed in detail in the thread New Post Notices are live network-wide on Meta Stack Exchange, as well as the linked blog posts and mother-meta threads.
In particular, this answer raises the specific complaint that the new off-topic closures don't show the specific closure sub-reason text which documents why the question was closed and which links to the site's further guidance about what to do in those scenarios, which absolutely, definitely breaks one of the key mechanisms of that this site has to communicate its scope to newcomers.
That answer is marked, as of this writing, as status-review by the SE dev team. Support of that answer (via votes on the answer and its comments, as well as civil, well-argued comments for why it's important) is probably the best (only?) way to make this change and change quickly.