Thanks @Hilbert-TP — glad to hear this has been escalated to engineering. To answer your question directly: yes, my camera was running exactly firmware 1.5.3 Build 260304 Rel.25729n immediately...

Thanks @Hilbert-TP. I have to be clear: Case 2 cannot work for this failure. It relies on the camera powering on, reconnecting to Wi-Fi and auto-re-downloading the firmware — but mine never boots...

Same issue as this thread — Tapo C320WS V2 (EU, HW 2.0) bricked by a failed OTA firmware update. It was running firmware 1.5.3 Build 260304 Rel.25729n when the update left it in an infinite bootloop...