I have the exact same problem. Using RC macOS, iOS and Xcode 26 and after archiving it won’t allow me to upload. Needs to be fixed ASAP because launch day is just in a few days and we need to submit our update to be available on day 1!

Same problem here. Using Xcode 26 beta 6 and the latest version of icon composer (checked today). If I get the icon composer exported icons and use Preview to remove the alpha channel, I can submit with no problems, but the whole point of icon composer is to have those transparency/Liquid Glass effects…