Hi,
Finally I got few minutes and I was flashing the OpenWRT uboot instead of stock one.
I have done step by step as it was in manual, (r03, 1.0.84, airoha drivers included) but in the end, router got a brick. What I get in UART:

U-Boot 2024.10-OpenWrt-r28641-7585abfb16 (Jan 19 2025 - 18:13:11 +0000)

CPU:   MediaTek MT7981
Model: Xiaomi Router AX3000T
DRAM:  256 MiB
Core:  39 devices, 17 uclasses, devicetree: embed
Loading Environment from UBI... spi-nand: spi_nand spi_nand@0: unknown raw ID cd 71 71 cd
Partition ubi not found!

** Cannot find mtd partition "ubi"
In:    serial@11002000
Out:   serial@11002000
Err:   serial@11002000
reset button found
Loading Environment from UBI... spi-nand: spi_nand spi_nand@0: unknown raw ID cd 71 71 cd
Partition ubi not found!

** Cannot find mtd partition "ubi"
Net:
Warning: ethernet@15100000 (eth0) using random MAC address - fe:88:00:af:61:20
eth0: ethernet@15100000
Error, no UBI device selected!
Error, no UBI device selected!
spi-nand: spi_nand spi_nand@0: unknown raw ID cd 71 71 cd
MTD device ubi not found, ret -19
resetting ...

F0: 102B 0000
FA: 1040 0000
FA: 1040 0000 [0200]
F9: 0000 0000
V0: 0000 0000 [0001]
00: 0000 0000
BP: 2400 0041 [0000]
G0: 1190 0000
EC: 0000 0000 [1000]
T0: 0000 0236 [010F]
Jump to BL

NOTICE:  BL2: v2.10.0	(release):OpenWrt v2024.01.17~bacca82a-3 (mt7981-spim-nand-ddr3)
NOTICE:  BL2: Built : 18:13:11, Jan 19 2025
NOTICE:  WDT: [40000000] Software reset (reboot)
NOTICE:  EMI: Using DDR3 settings
NOTICE:  EMI: Detected DRAM size: 256MB
NOTICE:  EMI: complex R/W mem test passed
NOTICE:  CPU: MT7981 (1300MHz)
NOTICE:  SPI_NAND parses attributes from parameter page.
NOTICE:  SPI_NAND Detected ID 0xcd
NOTICE:  Page size 2048, Block size 131072, size 134217728
NOTICE:  BL2: Booting BL31
NOTICE:  BL31: v2.10.0	(release):OpenWrt v2024.01.17~bacca82a-3 (mt7981-spim-nand-ddr3)
NOTICE:  BL31: Built : 18:13:11, Jan 19 2025


U-Boot 2024.10-OpenWrt-r28641-7585abfb16 (Jan 19 2025 - 18:13:11 +0000)

CPU:   MediaTek MT7981
Model: Xiaomi Router AX3000T
DRAM:  256 MiB
Core:  39 devices, 17 uclasses, devicetree: embed
Loading Environment from UBI... spi-nand: spi_nand spi_nand@0: unknown raw ID cd 71 71 cd
Partition ubi not found!

** Cannot find mtd partition "ubi"
In:    serial@11002000
Out:   serial@11002000
Err:   serial@11002000
reset button found
Loading Environment from UBI... spi-nand: spi_nand spi_nand@0: unknown raw ID cd 71 71 cd
Partition ubi not found!

** Cannot find mtd partition "ubi"
Net:
Warning: ethernet@15100000 (eth0) using random MAC address - 92:54:32:00:e7:e7
eth0: ethernet@15100000
Error, no UBI device selected!
Error, no UBI device selected!
spi-nand: spi_nand spi_nand@0: unknown raw ID cd 71 71 cd
MTD device ubi not found, ret -19
resetting ...

Is something what I can do or it will be a good beer mat?