Solved. For anyone who lands here with Xcode 27 Organizer "Validate App" / "Distribute App" stuck forever at "Preparing… Validating…" (Transporter.app too), with no error: The cause on my Mac was Rosetta. During validation, Xcode's swinfo helper asks for a tool called dwarfdump-classic. Xcode 27 no longer includes it, so macOS falls back to /Library/Developer/CommandLineTools. My Mac had an old Intel-only copy there from 2019 (carried over years ago by Migration Assistant). After a recent macOS update, Rosetta was no longer installed, so that old tool couldn't launch, and swinfo waits forever instead of reporting an error. What fixed it: sudo softwareupdate --install-rosetta: validation completed right away. Then I renamed the stale folder (sudo mv /Library/Developer/CommandLineTools /Library/Developer/CommandLineTools-old). Validation still passes: without the old copy, swinfo uses Xcode 27's own dwarfdump. Quick checks if you're stuck the same way: Does /Library/Developer/CommandLineTools/usr/bin/dwarfdump-classic exist, and is it Intel-only (file on it says x86_64 only)? Is Rosetta installed? (/Library/Apple/usr/libexec/oah/ should contain libRosettaRuntime.) What was not the cause, in my case: certificates, network, the archive, Apple ID, or the Xcode license.

Fixed for this build submission. Revoked certificates, reissued, bumped Xcode build number and archived again. Uploaded via terminal.

Keep trying, after 3 hours mine was finally accepted. I did Validate beforehand the last time I tried, doubtful that it helped, but it did complete afterwards.

This was resolved.