My tablet is bricked because the bootloader is locked

Hello. Here is my problem. I wanted to get rid of navigational bar to use gestures only (I didn’t know there was already such an option in the settings) and in order to do that I installed an app from PlayStore that claimed it would hide navigational buttons. The app required root access, so I provided root to the app. After the app did something, it asked to reboot the tablet, so I did it. After the tabled booted, I noticed that WiFi and camera doesn’t work. So I decided to reflash the tablet. I already had a custom rom intalled (PixelExperience Android 11 from xda-developers.com) so I thought there would be no huge problems with it. I wiped everything in recovery and did everything exactly as I did the previous time when I was flashing a custom rom (using adb). But it didn’t work out. So I tried using FlashTool which was also unsuccessful. In despair, I decided to try to lock and unlock the bootloader, but as soon as I locked it and typed reboot in adb the tabled turned off. It stopped turning on at all and even after connecting the charger there was nothing displaying on the screen. I know the tabled isn’t dead because after connecting it to a PC Windows makes a sound. I also tried flashing a rom via FlashTool with a battery taken out and on Linux too. Nothing worked. Any ideas how to solve this problem?
My tablet is Alldocube iPlay 30 (T1012E).

Generally speaking, as long as the MTK machine can be powered off and shut down, the firmware can be re-flashed with mtk flashtool.

Alldocube iPlay30 Pro(T1012E) firmware download

you can try to download firmware for T1012e here,and flash the firmware.