Xiaomi Mi 9T all of a sudden bricked - ADB shows "unauthorized device"

[sephSC]

Hello all,

my Xiaomi 9T bricked - no external force like a drop, I also never tinkered with flashing or something like that - I just heard a notification coming in, wanted to check on that and the phone just never turned on.
I tried getting it into Fastboot or Recovery mode, however no success. What I noticed was, that the phone was kind of recognized when i "booted" it into fastboot. I unfortuntately cant remember, if I turned on USB Debugging (think I did though) and installed ADB drivers to maybe get something done.

Unfortunately, all I get via ADB is "e42a47 unauthorized". Even after killing/starting ADB and deleting adb-files in .android folders. I don't know if my phone wants me to grant access, but since the display is black, I can't tell.

So if you have ANY ideas how to save the phone, I'll gladly try it out.

Thanks!

 

[sephSC]

I decided to try again and google some more. I discovered the "XiaoMiToolV2", tried to install a new ROM. I put the phone (still showing a completely black screen) into Recovery-Mode using Power and Vol+ and selected (blindly) the "reboot" option.

Now the phone seems to work normally, it shows up in Windows Explorer (although not showing files unfortunately - I guess its not in the right mode to do date transfer) and I also can hear the appropiate sounds when charging it/disconnecting it/etc - the screen still stays black.

Any idea where the problem could be? Is this more on the hardware side now?
As already being said, it never went black after a drop or anything (drops did happen in the past though).

e: It seems that the finger-print sensor is still working too.
I am now trying the almost legendary "rubber band"-method to drain the battery and see what happens.