I have an old Huawei P20 Pro floating around. When it was new, you could contact Huawei and get a code for unlocking the bootloader after providing your phone's serial number. Great I thought, I'll do that later when it stops receiving updates. Stupid me, at some point those arseholes stopped giving out the unlock codes. I wonder if one could sue, but from googling around a bit I can't find a trace of them ever making this a selling point explicitly.