i bought mine directly from google’s website. i am not 100% certain, but if you buy a phone from the manufacturer, i think it tends to be unlockable. it was literally a setting in developer mode to unlock the bootloader. my fairphone 6 (screenshotted) is the same. just don’t get the phone from your carrier, and probably not second hand unless you know its not locked to a carrier. you can probably find a forum for any phone youre interested in to see what the unlocking experience was like for other owners of that model

someone else posted a link to lineageos’s device compatibility, which implies and easily unlocked bootloader as well

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