It is widely known and has been discussed on here numerous times that Verizon disables the ability to unlock their device's OEM and bootloader and they claim to not be able to undo it. This is why it's stated on the GrapheneOS website that "devices sold in partnership with specific carriers may be locked by the carrier, which will prevent installing GrapheneOS. This is primarily an issue with US carriers and isn't common elsewhere in the world. To avoid this, either don't buy a carrier device, or make sure it can be unlocked. It's the same hardware/firmware/software either way but carriers dislike having devices able to bypass their paywall for tethering, etc., so they disable it for the devices they sell as part of contracts."
https://grapheneos.org/faq#device-support
More often than not, when a listing states that a device is "unlocked", it's referring to Carrier/Network.