I use ATC1441's UART flasher website: (https://atc1441.github.io/ATC_TLSR_Paper_UART_Flasher.html)

Baud rate 460800, 3s wait

Connect -> unlock -> select FW -> Write

!!! UNPLUG NRST IN THE ACTIVATION PHASE OF THE FLASHING !!!

If regular fw not working try the SSD version.