Google seems to be testing underlining the title, link and domain in the search result snippet when you hover your mouse cursor over the snippet. Generally, Google will just highlight the title link, the blue link, under the URL but here Google is underlining all of it.
We have seen Google Ads underline display URLs, Google Search underline title links by default and back in the super old days, the links were underlined always.
Sachin Patel spotted this and posted screenshots on X and I can replicate.
Here is a GIF of it in action:
Here is a static image:
Normally, only the blue title link will underline on hover.
Forum discussion at X.
