One of Google's most hidden messaging "clients" is the one built into YouTube. The feature was first privately tested as shared videos in May of 2016, but took more than a whole year to be available to everyone. It was then renamed to Messages and bundled with notifications in YouTube's Activity tab, but remained mobile-only until 2018 when it started showing up on the web. Now, the feature has been officially put on life-support and will be pronounced dead on September 18.
YouTube made the announcement yesterday, saying it decided to focus on its public conversations (comments, posts, stories) instead of private messages. Of course, some users are being very vocal about their discontent and the support thread has over 400 angry comments. That likely won't change much.
If you feel strongly about your YouTube chats, you can go to this address to back up your conversations. And be prepared for the feature to completely die on September 18, though some aspects of it may disappear before. After it's gone, you'll still be able to share video links, but you'll have to choose another social network or messaging app to send those with.
I can't say that I'll be missing YouTube messages all that much. I used it a bit at first, but with time, I gravitated back to sharing video links to my contacts on WhatsApp. It made more sense to keep all my conversation with them in one app, instead of spreading it all over the place.