Please translate into user language. Thanks.
An Application Program Interface (API) is essentially a list of the parts of a program (in this case, Bing search) that can be used by other programs, along with the definitions of any data that has to be supplied by the calling program. When something in an API has changed, the other programs that use it must also be changed; otherwise the existing call won't work and an error will occur.
The information that Suzanne quoted means that the Editor code has to be changed to match the new API of Bing search. The changes must be inspected and tested to avoid (or at least try to avoid) unintended trouble that could be caused by interactions with other code. Once that's done, the changes must be approved by managers in the Office, Bing, and Windows teams before it can be released. This was probably slowed by the fact that many Microsoft employees take vacation time in December.
Rather than let the Editor's Similarity Checker continue to display "something went wrong" messages that are caused by the mismatch between the Editor code and the new Bing API, the Similarity item in the Editor will be hidden until the approved changes are available.
But... In Microsoft 365 latest version (version 2312 Build 17126.20132 Current Channel) that I use, the Similarity Checker is still showing in the Editor and still giving the same message. Also, the Insider Channel release notes at https://learn.microsoft.com/en-us/officeupdates/update-history-beta-channel don't mention any change to Editor.