can you link a guide to flash custom firmware (lineageos) on debian on a redmi 9c or help me flash it?

cross-posted from: https://linux.community/post/1031833

most guides I found online are for windows based computers and those that even name linux are outdated.

• Linux distro I run: debian 12.5, adb and fastboot installed through apt

• Phone I want to experiment with: redmi 9c

• Firmware I'm installing: https://xdaforums.com/t/rom-13-unofficial-lineageos-20-0-unified-for-redmi-9a-9c-10a-blossom.4609367/

fastboot devices recognizes the device and I can also boot the phone to fastboot: it shows a black (not blank) screen with the word FASTBOOT printed orange.

I tried following https://android.gadgethacks.com/how-to/complete-guide-flashing-factory-images-android-using-fastboot-0175277/ but fastboot flashing unlock and fastboot oem unlock return FAILED (remote: 'Token Verify Failed, Reboot the device ')

developer options and OEM unlocking are both activated on the device