Huawei stopped providing official bootloader unlock codes years ago, so you will need a community tool.
The first boot takes 5-10 minutes. On LineageOS GSI, you must flash a "Huawei audio fix" via fastboot, otherwise speakers output static noise. huawei matepad 104 custom rom 2021
Flashing the downloaded GSI image file: fastboot flash system your_gsi_image.img Performing a factory data reset: fastboot -w Rebooting the device: fastboot reboot Better Alternatives to Flashing a ROM huawei matepad 104 custom rom 2021