Hovering a username mentioned in a comment now shows a huge "Send a message" button which presumably uses the off-the-track and not-best-practice Conpherence mechanism.
The button should be repurposed to link the user talk page, or have a second and bigger button "send a public message" next to it, or be removed entirely.
See Also:
T78238: Add optional "contact user" link to Phabricator user profiles