Dev Kit bricked after updating to Big Sur beta 7

Running fine on macOS 11 beta 3, then updated to 7 (had to reinstall the profile from the developer website); now it will not even boot. LED turns on for a few secs, then distinguishes, then again lights for a few seconds, etc. Doesn't even get to the Apple logo.
Dev Kit bricked after updating to Big Sur beta 7
 
 
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