Microsoft is testing changes to the top sites tiles in the New Tab Page on Edge.
The new icons are much smaller, though still the same in number.
They also now have a semi-transparent background vs an opaque background, as can be seen in the screenshot below.
It is speculated that the change is a precursor to Microsoft increasing the number of sites on the New Tab Page, making it more like a launcher for PWAs than a collection of site links.
Thanks, Leo for the tip.