In the beta of Icon Composer, I see macOS, iOS, and watchOS icons, but there is nothing about visionOS and tvOS. Those icons are particularly hard and it would be great if this app worked for developing icons for all Apple platforms.
I tried asking this in a WWDC group lab, but they didn't get to it and suggested posting to the forum.
We couldn't get to this question during the group lab session today, but we certainly saw it during the lab and appreciate you coming and asking about this!
As you found, Icon Composer supports iOS, macOS, and watchOS icons. For tvOS and visionOS, you can preview the icon in Xcode through your asset catalog, or by using the Parallax Previewer app available for download on the Apple Design Resources page.
I encourage you to create an Enhancement Request in Feedback Assistant for Icon Composer to gain support for visionOS and tvOS icons. Please post the FB number here!
— Ed Ford, DTS Engineer
