[Thinkpad Tablet Android Development] black.kahder:
Today I did some experiments with my tablet. I install the Lenovo LMSA app on a spare PC with Windows and did two full factory restores and custom ROM installations.

Below is my own set of improved installation instructions. These instructions worked for me and my TB-X704V and twrp-3.2.3-0-TB-X704F.img, but they might not be perfect for other models.

If you have improvements or corrections let me know and I will try to make it better.

Sorry for the strange indent format. BBCode makes indenting lists difficult. Maybe I will reformat later.

1.) Prepare

----A.) Backup all data on the tablet. Expect everything to be wiped.

----B.) Install the Android SDK tools. (adb and fastboot).

----C.) Download the custom ROM, TWRP, set_permissive.zip, Open GApps, Magisk

----D.) Set up your SD Card and copy your installation files there.

--------Do not use NTFS or HPFS for the SD Card format. Use fat32, exfat, or ext2/3/4.

2.) Unlock the bootloader in the OEM system Developer Options

----A.) Enable Developer Options, then "OEM unlocking" "Allow the bootloader to be unlocked".

--------https://developer.android.com/studio/debug/dev-options.html

----B.) Plug in the USB cable.

3.) Reboot into bootloader mode

----A.) Run command "adb reboot bootloader"

--------OR

--------Power off the tablet and boot into bootloader mode by holding vol-up + power.

4.) In bootloader/fastboot mode run command "fastboot oem unlock-go". The "DEVICE STATE" line on the bottom will change from "LOCKED" to "UNLOCKED".

5.) Run command "fastboot flash recovery twrp-3.2.3-0-TB-X704F.img".

6.) Use Volume button to select "Recovery mode" and press the power button to enter.

7.) The tablet should boot into TWRP.

----A.) WARNING: If the OEM system boots, it will replace TWRP with the OEM recovery. If this happens, start over at Step 3.

----B.) TWRP may prompt: "Unmodified System Partition" / "Keep System Read only?"

--------Swipe the "Swipe to Allow Modifications" to mount /system as writable.

--------Optionally select the checkbox "Never show this screen during boot again"

----C.) The TWRP UI may not work properly the first time.

--------On the first boot into TWRP, the UI may freeze up.

------------The top three rows of buttons won't work, or will only work sometimes.

--------If this happens, force the tablet off and back into bootloader mode by holding the power button and Volume-up button for 10-13 seconds.

------------Go back to Step 6 and continue. The UI should work the second time.

----D.) Format the /data partition.

-------- If you get "Failed to mount '/data' (Device or resource busy)" and "Unable to mount storage" errors, then reboot into TWRP again and repeat this step.

----E.) Install the custom System ROM and any additional zips. Remember to use the "Select Storage" button, use "Micro SD card".

----F.) Reboot.

8.) Lineage OS should now boot.

----The system will take awhile to set up. It will reboot twice as it needs to encrypt partitions, and then must compile the dalviks.

These instructions make notable changes to steps 4-6 and add workarounds for problems I encountered; The UI not working, and not being able to mount-format the /data partition. These issues are always resolved by restarting TWRP. Hopefully future versions of TWRP will resolve these problems.