Google is discontinuing the feature to post in your verified Google knowledge panels starting on July 20, 2021. This does not impact Google Posts within Google My Business but does impact those who used it on their knowledge panels.
As an FYI, Google started experimenting with posts on knowledge panels for sports teams back in 2017 then expanded it to artists back in 2018 and then it came to all verified knowledge panels later that year.
But now it is going away.
The Google help document has a notice at the top that reads "Posts on Google is going away on July 20, 2021. You can access and download your content until August 19th. You may continue to suggest edits to the knowledge panel."
Jason Barnard shared how it works before it goes away on Twitter saying "Posts to #knowledgepanel are going away. I thought I'd do one last post for my band before this "social" feature is retired."
Lily Ray shared this screenshot of an email she received from Google telling her it is going away:
So it is going away this coming Tuesday. I don't think I ever used it...
Forum discussion at Twitter.