Paul Kafasis has a nice run down of some of the worst icons in macOS Tahoe.
For my money, the single worst change is the photos app icon, shared across the OSs. The old icon did a great job of using transparency to mix the colors. The ovals are nice and sharp with high contrast to the white background. I constantly think something hasn’t loaded correctly with the new icon. The roundedness and specular highlights around the edges of the ovals lose the contrast with the background and suddenly the whole thing feels blurry.
At Ken 