This is still an issue on 26.3. @SubvertDev What I ended up doing was extracting the Icon Composer rendered icon variants from an Assets.car built with Xcode 26.0.1 and adding those back to the project as pre-rendered icons to the assets catalog. Updating the icons in the future will be a pain, but at least for now the app's compressed thinned size hasn't gone up by >20MB when building with Xcode 26.1 and later.

@SubvertDev I'm also seeing this same problem. What I've noticed in our app and the left-hand-side of the image you posted is that even on 26.0.1 the rendered icons are already duplicated, which already had a large impact on our binary size. 26.1.1 seems to quadruple them and make the binary size even larger.