Microsoft is testing a new design and user experience for the Bing sitelinks and related searches. The sitelinks he this hover over shadow effect, while the related searches go from a rounded pill design to line separator design.
Both of these were spotted by Sachin Patel.
He posted about the sitelinks change on X - notice the shadow/dark hover effect:
And the related searches go from a round pill design to this line separator design:
Forum discussion at threads above.