Right, afaik the Murena offer is the one option to get the Fairphone 6 in the US. I would be very surprised if the bootloader is not unlockable. Bootloader locked is likely meant as something positive: They installed /e/ and then were able to relock the bootloader. You should be able to do the same - but yeah, I would double check that with them before buying, given the price...

Lineage has no account system. /e/ does, optionally.