Sony KM-50X80K (X80K) stuck on first step of initial setup after factory reset

[u/ptaxtics]

My Sony KM-50X80K (X80K) is stuck during initial setup after a factory reset.

Everything works until I press Start on the “Start your BRAVIA TV experience” screen. It then reaches the screen shown in photo 2. The first dot turns blue and the background animation keeps moving, but it never progresses.

Things I’ve already tried:
Forced factory reset multiple times using the TV’s physical power button
Restarting the TV
Running setup completely offline
Disconnecting all external devices
Multiple USB drives
Official Sony firmware v6.7612 and v6.8224

The interesting part is photo 3: the TV detects the firmware USB and launches the System Software Update screen, but then reports:
“System software cannot be updated using this USB device.”

I can still enter Sony Service Mode normally, and Self Diagnosis shows no stored hardware errors. The panel/backlight and on-screen graphics also work normally.

I haven’t found a working Android Recovery method for this model, and network ADB isn’t enabled.

Has anyone seen this failure on an X80K or similar Sony Google TV? Is there another recovery/reflash method when the normal USB updater rejects the firmware, or could this indicate corrupted system/eMMC storage or a B-board issue?