Huawei stopped providing bootloader unlock codes around 2018. The NMOL31 likely has a locked bootloader, making custom ROM installation impossible on stock firmware.
: Rooting or flashing custom software on Huawei devices carries a high risk of "bricking" the device, especially given Huawei's restrictive bootloader policies. Always back up your data before proceeding. for your Huawei bootloader? huawei nmol31 custom rom verified