Thanks, @maycontainthunder, I've just spent a little bit of time looking into whether this is an option that I'm able to change as I also found it useful as then I could see a notification without having to leave the page, however, it looks like this is a decision that the XenForo developers made consciously. There was briefly an addon to bring the functionality back but it has now been removed.Ah, cracked it. It only displays the popup and does not load anything else. When you click on the user ID on the popup then it goes to the profile page itself. The old popup version had a link to the profile page.
Something else to adjust to is the alerts system. Before I would hover the cursor over the alert 'bell' to display the alerts. Now I have to click on it.
I think everyone is going to have a few days of adjusting to the different way the new version 'behaves'.
Thank you for your efforts Satal.
BTW on an unrelated note, I do like the middle line of your signature and I'm tempted to add it myself.