Xiaomi Mi 9T installation problems

Hello everyone,

I have got a Xiaomi Mi 9T purchased to run with NetHunter (saw it was suggested as mid class device).

This is what I have done:

- Flash full OTA, from Xiaomi site got only MIUI 12.0.2 ---> all OK
- Flash TWRP 3.4.0.0 via Fastboot ---> all OK
- Flash Magisk 20.4 zip via TWRP ---> all OK

From now on got some trouble:

- Flash DM-verity and encryption disabler ---> seems to be all ok, device was unencrypted but some time TWRP, when after flashing something else, logs some problems about FBE encryption.
- Flash Nethunter Davinci image downloaded from Offensive official site ---> after rebooting system alert about some big problems in the OS suggesting to contact the factory. Nethunter wallpaper is installed but I can't find all the other apps, if I open Magisk app now it says that also Magisk is not present in the system and from now on there are only troubles. The only way to return to normally is to flash the OTA.

I can't understand what I am doing wrong... I read a lot of people saying that they didn't have any issues installing this device...
I have also tried to do things in different order, i tried to search internet for similar issues, nothing..

The only thing that comes in my mind is that I saw an "antivirus" app in the stock OTA (named security), maybe it detects NetHunter's stuff?
I also see that official documentation speaks about MIUI 11 and not 12 but I was not able to find a secure MIUI 11 OTA.

Thanks in advance for you help.

Futu