What is Icon Composer?
It's the app added in XCode 26 for making icons work with liquid glass.
It gets installed automatically as part of the app when you download the latest XCode.
How to use it
It's really simple to use — you just add a background transparency image.
In my case, I'd built an app whose shader changes in sync with a piece of music called Sonivium, so I decided to try it out with this icon.
Once you add it in Icon Composer, you can switch the icon's Fill setting between solid and gradient from the Fill menu.
I decided to go with gradient.
You can change the background color the same way.
It also supports dark mode and translucent modes.