I'm stuck on the first step in getting to install UnbuntuTouch on my Lenovo x606F, the dpwngrade from Android 10 to Android9 I am not used to Android and have never tried to reflash an Android device before; all the threads I can find on the topic seem very specific to particular versions of flashing software and device.
So, I am using

1. Manjaro Linux (I don't have a Windows system)
2. SP_Flash_Tool_v5.2152_Linux (I can't use the most recent versions of the flash tool, as they expect an xml file for download, instead of the scatter.txt file that Android 9 has)
3. Lenovo_Tab_M10_FHD_Plus_TB-X606F_MT6765_S000009_210526_BMP as my Android9 image.

I can't get the Flash Tool to write anything to the tablet at all; I have tried both starting with the tablet off and holding down volume and/or power while connecting the USB, and using 'adb reboot fastboot' after starting download on the Flash Tool. Whichever I do I get the same result:

./flash_tool.sh
QGtkStyle was unable to detect the current GTK+ theme.
sysname:Linux
 nodename:gromit
 release:5.15.89-1-MANJARO
 version:#1 SMP PREEMPT Wed Jan 18 20:37:11 UTC 2023
 machine:x86_64

  domainame:(none)
 cur_kernel_version = 5.15.89
QObject::moveToThread: Cannot move objects with a parent
support_dl_cert_to_storage: 0
Application asked to unregister timer 0xa00001b which is not registered in this thread. Fix application.
Connecting to BROM...
Scanning USB port...
 Search usb, timeout set as 3600000 ms
add@/devices/pci0000:00/0000:00:08.1/0000:04:00.3/usb1/1-2
add@/devices/pci0000:00/0000:00:08.1/0000:04:00.3/usb1/1-2/1-2:1.1
add@/devices/pci0000:00/0000:00:08.1/0000:04:00.3/usb1/1-2/1-2:1.0
bind@/devices/pci0000:00/0000:00:08.1/0000:04:00.3/usb1/1-2/1-2:1.1
add@/devices/pci0000:00/0000:00:08.1/0000:04:00.3/usb1/1-2/1-2:1.0/tty/ttyACM0
vid is 0e8d
device vid = 0e8d
device vid = 0e8d
pid is 2000
device pid = 2000
com portName is: /dev/ttyACM0
Total wait time = -1675547049.000000
USB port is obtained. path name(/dev/ttyACM0), port name(/dev/ttyACM0)
USB port detected: /dev/ttyACM0
Connect BROM failed: STATUS_ERR(-1073676287)
Disconnect!
BROM Exception! ( ERROR : STATUS_ERR (-1073676287) , MSP ERROE CODE : 0x00.
[HINT]:
)((ConnectBROM,../../../flashtool/Conn/Connection.cpp,105))

The tablet itself reports that it is in fastboot mode.

Any ideas?
Thanks
Graham