I finally figured out how to port a TWRP for this device.
This is for the Lenovo tab M8 FHD TB-8705F running the following version TB_8705F_S300022_201015_BMP
Please find the file attached here.
To make this work you will need to flash the vbmeta.img with the option --disable-verification. Some say you need the vbmeta.img to be an empty image file I'm attaching such a file here as well.
Use this at your own peril.
If you would like to try your hand at porting it yourself I used This guide. It was very helpful.
Hi. I did it successfully with @Isrgish unofficial TWRP port for 8705f the same way I've flashed the patched boot.img while rooting the device. It means that it works with the unmodified vbmeta.img already extracted from the "TB_8705F_S300022_201015_BMP_SVC" Rom files:
1. flash the TWRP port to recovery
fastboot flash recovery twrp-3.4.0-mod-isrgish_tab-m8-fhd-8705f.img
2. flash vbmeta.img
fastboot --disable-verification flash vbmeta vbmeta.img
3. flash the TWRP port to recovery again
4. reboot with
Then power off the tablet and start it again in recovery mode (Volume Up + Power). Well done!
I've also installed "Power App | Simple Power Menu [Root only]" from F-Droid so I'm able to reboot to recovery directly from Android.
- I've faced a first screen titled "Mount - Decrypt Data" with a blank password field. But the encryption is Lenovo-made and I have no idea of any kind of password. So I hit Cancel. And I swipe right to allow modifications to system partition.
So come the well-known TWRP interface with big square buttons.
- I've tried to wipe the Dalvik / ART Cache and it shown errors like :
"Failed to decrypt data. Unable to decrypt data with default password. You may need to perform a Format Data."
"Unable to mount storage"
"Full SELinux support is present" (my fault, didn't yet switch it to permissive mode)
So system backups are impossible too because partitions can't be mounted. As long as there's no XDA forum for this model with AOSP or Lineage custom Roms, I don't want to modify things too deeply just to get access to encrypted partitions. Not sure but disabling encryption looks impossible to me without formatting. And a Lenovo firmware update would surely encrypt it again or do fancy things after reboot even if "switching" encryption off would be possible. What do you all think about it?
Anyway, in spite of the error messages, flashing the latest Magisk update worked fine. I just had to put the ZIP file in a directory that is accessible from TWRP (ie. /cache).
Thanks again @Isrgish for sharing your work!