LineageOS does not support unlocking the bootloader on any Google Pixel device. Other Android CustomROM distributions, however, do, e.g. CalyxOS, iodéOS, GrapheneOS.
Yeah, the /e/documentation is very buggy. I only use it to test it. Otherwise I install /e/OS my way.
It’s strange that an device-specific ‘avb custom key’ of the Google Pixel 5 (redfin) is identical to that of the Google Pixel 4 (flame) und Pixel 4 XL (coral):
** identical file name, identical download URL:**
P 5 (redfin): 2. Download the avb custom key
https:// images.ecloud.global/stable/pkmd_pixel
P 4 (flame) 2: Download the avb custom key
https:// images.ecloud.global/stable/pkmd_pixel
P 4 XL (coral) 2: Download the avb custom key