twrp-3.2.1-2-ttab.img gets stuck in reboot loop, trying to protect against stock bootloader override. This one works:

https://eu.dl.twrp.me/ttab/twrp-3.2.1-1-ttab.img.html

adb reboot bootloader
fastboot oem unlock
fastboot reboot
adb reboot bootloader
fastboot flash recovery /path/to/twrp.img
fastboot reboot
adb reboot recovery

First format everything, including /data !

Go to Recovery: Volume UP + Power

Download Lineage: https://lineage.stricted.net/ttab

Copy OS img to the tablet:

adb push /home/tk/dl/lineage-14.1-20180520-UNOFFICIAL-ttab.zip /data/

Click Install in TWRP

Wipe everything again and reboot

The first boot takes ~10min

Lineage & TWRP:

https://www.android-hilfe.de/forum/alcatel-telekom-puls-by-alcatel.2440/rom-unofficial-ttab-7-1-lineageos-14-1.875266.html

Stock ROM and recovery.img:

https://www.android-hilfe.de/forum/alcatel-telekom-puls-by-alcatel.2440/puls-software-flashen-reparieren-nuetzliche-links.733834.html