Please consider this as a privilege/perk for logged-in users (they can still visit the topic pages to view them). It's a reminder for them to be logged-in to use the feature. This is to differentiate features between logged-in users and Guests (similar to Pricing Plans that have "always free" tier).
Many sites restrict features like Search, etc. for logged-in users only. "Hover Popup UI for Guests" may be offered as an option in ACP with a switch (default: ON - won't alter current behavior) so site operators can turn it off as per their preference. If turned off, you could display "Login to use the popup feature" in the popup instead (or no popup at all).
This switch may be reused consistently for Hover Popup UI on Articles, Blogs, Events, etc:
Hover popup UI for other content types