1. Switch to vector icons (*.svg)
Vector graphics scale well and are small in size.
2. Drop pixel-fitting
GNOME and KDE uses one fullcolor one instead of several icons of different sizes. GNOME also use symbolic icon for sizes smaller than 32px.
Yaru already have symbolic icons for apps. Now we need to remove small icons.
3. Remove highlights
Highlights never wasn’t in Unity 8 icons.
So they look more minimalistic and more looks like paper.
4. New way to create Ubuntu icons
This way was used in Unity 8 and is used in iOS and Android adaptive icons.
Developer create full height and weight image. Shell with extension applies the mask.