https://www.engadget.com/2012-09-25-verizon-wont-relock-the-iphone-5s-gsm.html
Verizon won't relock the iPhone 5's GSM
verizoniphonegsm
https://discuss.grapheneos.org/d/270-relock-the-bootloader
Relock the bootloader - GrapheneOS Discussion Forum
GrapheneOS discussion forum
bootloadergrapheneosdiscussionforum