My PW3 was "bricked" aka stuck in Muscat_WCF diagnostics and with some fiddling ended up with Diags "please use serial port" message (perma ultra stuck).
Here is a solution that works:
Code:
https://www.mobileread.com/forums/showthread.php?t=231823
Just a heads up so you don't lose 3-4 hours sifting through 1000x of useless threads and suggestions where some people recommend sending your device back to amazon, opening your kindle, changing your battery etc.
It takes like 5 minutes to install virtual box so give it a shot. Kubrick probably works, too - however it's confusing since it's mentioned 100x that it DOESN'T work with paperwhites , so...