Steps to reproduce:
Bookmarking a site with a low-res favicon puts a super fuzzy upscale version on the start screen, which doesn’t look very nice. eBay and shopgoodwill in the picture below have small favicons.
I’m not sure, safari replaces the favicon with a filler icon if it’s too small or unavailable. Maybe that or some similar effect to avoid stretching a tiny image on the start screen.
Orion and iOS:
Orion 1.0.3 (102), iOS 15.1.1