Teclast M89 is a tablet by chinese company Teclast.
Teclast M89 firmware v2.13 for China region (no Google services):
Teclast M89 firmware v2.13 Global (with Google services):
These are original official firmware archives received from Teclast. Installation instructions and all the needed utilities and drivers are included into archive.
TWRP 3.3.1 for Teclast M89
The archive includes:
Teclast M89 uses well-known firmware signature Android keys (test keys), that's why you can flash TWRP without unlocking the bootloader and erasing user data. Installation instruction is inside the archive.
Teclast M89 issues (v2.13_20180907 firmware):
If your device boots only into TWRP after wiping, execute the following command while booted into TWRP, either from TWRP terminal itself or from adb shell:
dd if=/dev/zero of=/dev/block/platform/mtk-msdc.0/11230000.MSDC0/by-name/para
It seems OEM unlock fills "para" partition with some data which forces it to boot into recovery. Stock recovery reads this data and perform data partition wipe or something similar, but TWRP does not handle this data and you get a boot loop. You can fix that by cleaning "para" partition.