kindle 8th stuck in bootloop and no serial connection

[mattep91]

Hello everybody! I need some help in trying fixing my kindle 8th (serial number starts with G000K9). Here is the whole story:
A few months ago, the device started going into a bootloop, restarting until the battery was completely drained. I left the device untouched for a few months, until about a month ago, when I decided to try to fix it. After doing some research online, I found this guide that explains how to solve the problem on a different Kindle model, and by investigating further, I found this other guide that explains how to connect to the device via a serial port. So, I opened the Kindle and left it with the battery disconnected for a couple of weeks while waiting to receive all the necessary parts to make the connection as described in the second guide.
Once everything arrived, I made the connections as instructed and installed on my PC Minicom to communicate with the device. My PC runs Ubuntu 24.04 as the operating system.
At this point, after after leaving the battery disconnected for a few weeks, when pressing the power button the device sometimes goes into a bootloop, and other times it stays fixed on the tree picture.

However, after connecting the device to the PC through the serial-USB adapter, when I run the command:

sudo dmesg | grep tty

I get

[    0.091101] printk: legacy console [tty0] enabled
[  312.052189] ftdi_sio ttyUSB0: Unable to read latency timer: -32
[  312.054748] usb 2-2: FTDI USB Serial Device converter now attached to ttyUSB0
[  316.689930] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[  345.540067] ftdi_sio ttyUSB0: Unable to read latency timer: -32
[  345.540355] usb 2-2: FTDI USB Serial Device converter now attached to ttyUSB0
[  406.118527] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[  407.482293] ftdi_sio ttyUSB0: Unable to read latency timer: -32
[  407.482950] usb 2-1: FTDI USB Serial Device converter now attached to ttyUSB0
[ 1109.651438] ftdi_sio ttyUSB0: error from flowcontrol urb
[ 1109.651617] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[ 1236.056385] ftdi_sio ttyUSB0: Unable to read latency timer: -32
[ 1236.057143] usb 2-1: FTDI USB Serial Device converter now attached to ttyUSB0
[ 1530.484396] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[ 2002.953529] ftdi_sio ttyUSB0: Unable to read latency timer: -32
[ 2002.954259] usb 2-1: FTDI USB Serial Device converter now attached to ttyUSB0

Which already is not so promising.
So, after launching Minicom and entering in the serial device setting

/dev/ttyUSB0

I get:

Welcome to minicom 2.9

OPTIONS: I18n                                                                
Port /dev/ttyUSB0, 22:54:17                                                  
                                                                             
Press CTRL-A Z for help on special keys

...basically nothing appears. When I press the power button to turn on the Kindle, I get random symbols like:

�!�!�=!;!!�������￟���;!!���iKm�P5J��-�y=9/5�#!�5#=;'57��YY^����U�-���uOWyYw��^U#
�/5'���;!!����K.9SZKm�P5J��������������y_U���#�9!%%=#7��iK-�+����=���eo      
�/5'���;!!����K.9           #�9!%%=#7���K.9l+�

I also installed Win10 on a virtual machine and tried connecting the Kindle from there using Tera Term, and I get the same thing, but the string of symbols is longer and the device seems to go into a boot loop.

I then tried another route, reading this i soldered the two wires (with male/female connector for shorting/opening the connection) between the pins showed in the first image of the post. When connecting through USB with the connection shorted Ubuntu kind of see the device but only for a few seconds from the disk utility, without mounting it.

So my question is, is it possible to somehow recover the device? I kind of understood that it might be possible using Mfgtools, but I don't have any experience with it, and so I have no idea where to start.
Any help would be very much appreciated!

Sorry for the very long post!