FYI
After Sept. 18, you’ll no longer be able to send or receive direct messages on YouTube as we focus our efforts on public convo tools (comments, posts, etc).
You can still share what you’re watching w/ others via the Share icon below videos.
More→ https://yt.be/help/9Hns
Didn't you remove that feature years ago? You kept making it harder and harder to find with each update, then used the excuse "durr no one's using this anymore" to take it down. I never got notifications for direct messages either, so I had no way of knowing.