It seems that the upgrade from Tahoe 26.01 to 26.2 broke cross-architecture builds using Rancher Desktop using VZ with VZ Rosetta support enabled...

In the latest version of Xcode, you can simply edit the file /Applications/Xcode.app/Contents/SharedFrameworks/ContentDeliveryServices.framework/Versions/A/itms/java/conf/net.properties accordingly. After changing the following line (which is set to false by default), notarization was able to connect from behind out proxy server. java.net.useSystemProxies=true