Dead Poco M3

Hello guys.

I have a poco m3. I updated the ROM to PixelExperience. But the device sometimes restarts.

I tried to reinstall Stock ROM. I did something wrong ( I don´t know what). I used Xiaomi Flash Tool to restore to stock.

Now this is my phone.



I can still boot on FASTBOOT. But when I try to flash again it says can´t flash on a locked bootloader....

What to do?
Thanks