TL;DR. Metadata Manager will be retired at the end of 2025. Over the past four years, we have been developing a new helper tool to replace it, and that tool has now reached a stage of maturity that means we will be able to switch off Metadata Manager by the end of the year.
This is a companion discussion topic for the original entry at https://www.crossref.org/blog/the-sunset-is-on-the-horizon-for-metadata-manager.-whats-next